Reflective liquid crystal display device and reflective liquid crystal display device incorporating touch panel arranged therefrom

ABSTRACT

A reflective color liquid crystal display device with a liquid crystal layer sandwiched between a first substrate having a light reflectibility and a second substrate having a light transmissibility. The liquid crystal layer being composed of twist-aligned nematic liquid crystal having a positive dielectric anisotropy. A circularly polarizing unit, including a single linear polarizer plate, selectively passes either right handed or left handed circularly polarized light out of natural light. The circularly polarizing unit is disposed so that a major surface of the circularly polarizing unit is on a liquid crystal layer side, the circularly polarized light exiting the circularly polarizing unit through the major surface when natural light enters the circularly polarizing unit. Various parameters of the liquid crystal layer are optimized for a liquid crystal layer having a twist angle in the range of 0° to 100°.

This application is a Divisional of application Ser. No. 10/804,109,filed on Mar. 19, 2004 now U.S. Pat. No. 6,922,220, which is aDivisional of application Ser. No. 09/403,487 filed on Oct. 22, 1999 nowU.S. Pat. No. 6,791,640 and for which priority is claimed under 35U.S.C. §120. Application Ser. No. 09/403,487 is the national phase ofPCT International Application No. PCT/JP98/01348 filed on Mar. 26, 1998under 35 U.S.C. §371. The entire contents of each of theabove-identified applications are hereby incorporated by reference. Thisapplication also claims priority of Application No. 9-105518 filed inJapan on Apr. 23, 1997 under 35 U.S.C. §119.

TECHNICAL FIELD

The present invention relates to reflective liquid crystal displaydevices for direct view application used in wordprocessors, laptoppersonal computers, and other office machinery, as well as in a varietyof visual and game machines, without a need for a backlight, and alsorelates to such reflective liquid crystal display devices incorporatinga touch panel arranged therefrom.

BACKGROUND ART

Liquid crystal display devices, being characterized by their thinnessand light weight, have successfully found commercial applications ascolor display devices. Among these color liquid crystal display devices,transmissive liquid crystal display devices provided with a light sourcefor illumination from behind are in particularly widespread use, and areadopted for an increasingly wider variety of applications because of theabove-mentioned features.

In contrast to the transmission liquid crystal display device, thereflective liquid crystal display device does not require a backlightfor display, and therefore can reduce the power consumption of the lightsource. The exclusion of the backlight further characterizes thereflective liquid crystal display device by allowing it to be morecompact and lightweight.

In other words, in comparison to conventional transmissive liquidcrystal display, the reflective liquid crystal display device can lowerthe power consumption, and be suitably used in equipment which needs tobe lightweight and thin. For example, if the equipment with thereflective liquid crystal display device is designed while retainingconventional operation time, the reflective liquid crystal displaydevice can not only cut down on the backlight space and weight, butconsumes less power, and becomes capable of running on a smallerbattery, making it possible to further reduce the size and weight. Ifthe equipment with the reflective liquid crystal display device ismanufactured while retaining conventional size or weight, use of alarger battery is expected to increase operation time dramatically.

In addition, as to display contrast properties, the light emittingdisplay device, such as the CRT, degrades greatly in contrast ratio whenused outdoors during the daytime. Even the transmissive liquid crystaldisplay device subjected to a low reflection treatment inevitablysuffers similarly from greatly decreased contrast ratios when used inambient light, such as direct sunlight, that is excessively strongcompared to display light.

In contrast, with the reflective liquid crystal display device, thedisplay light obtained is proportional to the amount of ambient light,which is an especially suitable feature for application in a personaldigital tool, a digital still camera, a portable camcorder, and otherdevices that are often used outdoors.

When considering these potential application fields, the reflectivecolor liquid crystal display device appears very promising; however, arelatively low contrast ratio and reflectance, as well as insufficientperformances in multi-color, high precision, and moving picture display,have so far been obstacles in realizing commercially viable reflectivecolor liquid crystal display device.

The following description will explain the reflective liquid crystaldisplay device in further detail. The conventional twisted nematic (TN)type liquid crystal element includes two linear polarizer plates(hereinafter, will be simply referred to as polarizer plates), andtherefore boasts an excellent contrast ratio and viewing angledependency property; however, the reflectance is inevitably low. Inaddition, since the liquid crystal modulation layer is separated fromthe light reflective layer by a distance equivalent to the thickness ofa substrate, etc., there occurs parallax due to a disparity betweenincoming and outgoing optical paths of illumination light. Therefore,especially in a typical arrangement used for transmissive liquid crystaldisplay devices where a single liquid crystal modulation layer iscombined with a color filter that includes a separate subpixel for eachcolor element, provided that light does not travel parallel to thenormal to the substrate, ambient light enters and exits after reflectionthrough different color subpixels. This causes moire and otherundesirable phenomena, rendering the transmissive liquid crystal displaydevice unsuited for high resolution, high precision, color display use.

For these reasons, no reflective color display device using this displaymode has so far been commercialized.

Meanwhile, Guest-Host type liquid crystal elements (hereinafter, will beabbreviated as GH) have been developed that uses no or only onepolarizer plate and includes liquid crystalline material doped withdyestuff. However, the GH type liquid crystal element is not highlyreliable due to the addition of the dye, and the low dichroic ratio ofthe dye cannot produce a high contrast ratio.

Among these problems, the insufficient contrast level in particularcauses serious degradation in color purity and creates a need toincorporate a color filter of high color purity in a color displaydevice using a color filter. This entails a problem of reducedbrightness caused by the color filter of high color purity, and cancelsto some degree the advantage of this mode that high brightness isachieved by use of no polarizer plates.

On these backgrounds, research and development is under way tosuccessfully manufacture a liquid crystal display element in a mode inwhich a single polarizer plate is used (hereinafter, will be referred toas a single polarizer plate mode), which is highly promising to realizea high resolution and high contrast display.

Japanese Laid-Open Patent Application No. 55-48733/1980 (Tokukaisho55-48733) discloses such an example of a liquid crystal display elementof a reflective TN mode (45°-twisted type) using a single polarizerplate and a quarter-wave plate.

With this liquid crystal display device, black and white display isperformed, using a 45°-twisted liquid crystal layer and controlling theelectric field applied thereacross, by realizing two states, in one ofwhich the plane of polarization of incoming linearly polarized incidentlight is parallel to the optical axis of the quarter-wave plate and inthe other of which the plane of polarization forms 45° with the opticalaxis of the quarter wave plate. The liquid crystal cell is structured toinclude a polarizer, a 45°-twisted liquid crystal cell, a quarter-waveplate, and a reflector plate, when viewed from the side at which lightenters.

Further, U.S. Pat. No. 4,701,028 (Clerc et al.) discloses a liquidcrystal display device of a reflective-type, homeotropic alignment modewherein a combination of a single polarizer plate, a quarter-wave plate,and a perpendicularly aligned liquid crystal cell is used.

Meanwhile, the inventors of the present application filed an applicationfor a reflective-type, parallel alignment mode wherein a combination ofa single polarizer plate, a homogeneous alignment liquid crystal cell,and an optical retardation compensation plate is used (see JapaneseLaid-Open Patent Application No. 6-167708/1994 (Tokukaihei 6-167708)).

This reflective liquid crystal display device includes a liquid crystalcell constituted by a homogeneously-aligned liquid crystal layer, areflector plate (disposed inside the liquid crystal cell beneath theliquid crystal layer), a polarizer plate (disposed on the liquid crystalcell), and a single optical retardation compensator plate (placedbetween the liquid crystal cell and the polarizer plate). Further,according to this display mode, throughout the total length of theoptical path, i.e., the incoming optical path and the outgoing opticalpath, light passes through the polarizer plate only twice and throughthe transparent electrode where light is inevitably absorbed on a glasssubstrate (top substrate) of the liquid crystal cell also only twice.Therefore, a high reflectance can be obtained by means of a reflectiveliquid crystal display device of this structure.

Further, Japanese Laid-Open Patent Application No. 2-236523/1990(Tokukaihei 2-236523) discloses an arrangement in which a twistednematic liquid crystal layer is interposed between a reflector plate(disposed inside a liquid crystal cell) and a single polarizer plate.

Further, Fourth Asian Symposium on Information Display (Chung-Kuang Weiet al., Proceedings of The Fourth Asian Symposium on InformationDisplay, 1997, page 25; hereinafter will be abbreviated as ASID 97)discloses an arrangement wherein 90°-twisted nematic liquid crystal isinterposed between a reflector plate disposed inside the cell and acombination of a quarter-wave plate and a polarizer plate which realizesa broad band display.

In addition, Japanese Laid-Open Patent Application No. 4-116515/1992(Tokukaihei 4-116515) discloses a liquid crystal display device whereinincident circularly polarized light is used for display. In addition, asa method of obtaining circularly polarized light in a broad band ofspectrum, Pancharatnam teaches the use of a plurality of opticalretardation compensator plates in Proc. Ind. Acad. Sci. Vol. XLI, No. 4,Sec. A, page 130, 1955.

The description below will explain display principles of a singlepolarizer plate mode employed in ASID 97 and in the Japanese Laid-OpenPatent Applications No. 6-167708/1994, No. 2-236523/1990, and4-116515/1992.

The polarizer plate disposed on the side where light enters serves topass only one of the linearly polarized light components of the incomingand outgoing polarized light and absorb the other linearly polarizedlight component. The polarization state of the incoming light that haspassed through the polarizer plate is then changed by an opticalretardation compensator plate, such as a quarter-wave plate (in thecases of Japanese Laid-Open Patent Application No. 6-167708/1994 andASID 97), or remains unchanged (in the case of Japanese Laid-Open PatentApplication No. 2-236523/1990), and the light enters the liquid crystallayer. The polarization state is changed further as the light passesthrough the liquid crystal layer, before the light reaches a reflectorplate.

Further, the light that has reached the reflector plate changes itspolarization state in the reverse sequence to that of the incominglight: the light passes through the liquid crystal layer, thequarter-wave plate, etc. Consequently, the ratio of the linearlypolarized light component in a transmission direction of the polarizerplate to the light obtained here will decide the total reflectance ofthe liquid crystal layer. In other words, the liquid crystal displayelement appears brightest when the outgoing light, immediately beforepassing through the polarizer plate, is linearly polarized in thetransmission direction of the polarizer plate, and darkest when linearlypolarized in the absorptive direction of the polarizer plate.

It is known that the necessary and sufficient condition for the lightwhich enters and leaves the liquid crystal display deviceperpendicularly to the device to realize such a bright state is that thelight be linearly polarized in an arbitrary direction on the reflectorplate, and that for it to realize such a dark state is that the light becircularly polarized either right handed or left handed on the reflectorplate.

Meanwhile, a touch panel, as well as a conventional keyboard, is a veryuseful input means incorporated in a personal digital tool. This isespecially true in inputting such languages including Japanese thatkeyboard inputs need to be converted; with increasing informationprocessing capability and newly developed software, the touch panel,which used to serve simply as a pointing device, now more typicallyplays a greater role as an input device such as a pen-based handwritinginput device.

To realize this particular input method, the input device is disposed tooverlap the front of the display device. However, since the reflectiveliquid crystal display device uses reflected light for display, themeans to reduce reflection provided to the touch panel should notinterrupt display image produced by the underlying reflective liquidcrystal display device. For example, Japanese Laid-Open PatentApplication No. 5-127822/1993 (Tokukaihei 5-127822) discloses that atouch panel, a quarter-wave plate, and a polarizer plate are stackedtogether to reduce reflection.

Among the aforementioned conventional techniques, the liquid crystaldisplay device disclosed in Japanese Laid-Open Patent Application No.55-48733/1980 is not suitable for a high resolution, high precisiondisplay, because despite the need to provide a quarter-wave platebetween a liquid crystal layer and a reflector plate, it is difficultessentially to form a reflective film inside the liquid crystal cell.

In addition, the liquid crystal display device that operates in thehomeotropic alignment mode disclosed in U.S. Pat. No. 4,701,028 hasfollowing problems. The homeotropic alignment, especially the inclinedhomeotropic alignment, is extremely difficult to control, and thecontrol requires such a complex arrangement that is not suitable formass production. Another shortcoming of the homeotropic alignment is itsslow response.

In addition, coloring occurs with the aforementioned reflective-typeparallel alignment mode due to small unevenness of the liquid crystalcell and the optical retardation compensator plate. The conventionalarrangements, as discussed here, are likely to suffer from coloring in adark state and failure to realize black and white display.

In addition, the arrangements disclosed in Japanese Laid-Open PatentApplication No. 2-236523/1990 and Japanese Laid-Open Patent ApplicationNo. 4-116515/1992, although being capable of increasing the reflectionin a bright state in comparison to the arrangement using two polarizerplates, still fail to realize a good black display due to greatwavelength dependency of transmittance in a dark state.

In addition, ASID 97, although disclosing a display mode that enables ablack and white display, does not disclose anything about thearrangement of the quarter-wave plate which is, described in thisliterature, to be fabricated for a broad band of spectrum.

In addition, according to a report made by Pancharatnam, three opticalretardation compensator plates are required to obtain good circularlypolarized light, which is not practical. In addition, detailed studiesare yet to be made to combine this with liquid crystal display devices.

In contrast, the touch-panel-incorporating reflective liquid crystaldisplay device, although its performance as a reflective liquid crystaldisplay device has reached to a stage where it can be commercialized,still suffers from extremely poor visibility when used in a combinationwith a touch panel.

This is because, in the reflective display device, a single light sourceplays dual roles to cause reflection at the touch panel and to serve asa display light source for the display device, and decrease invisibility when used in a combination with a touch panel cannot besolved by removing the light that radiates from a light source (forexample, a ceiling light) which cause reflection at the touch panel, orchanging the direction of the light. This is a stark contrast to thetransmissive liquid crystal display device and other light-emittingtypes of display devices with which this solution produces good results.A conclusion drawn from here is that the solution to the poor visibilityis a key to a successful commercialization of the display device, aswell as to that of a practical, low power consuming personal digitaltool.

In addition, the arrangement of the touch panel disclosed in JapaneseLaid-Open Patent Application No. 5-127822/1993 is effective inpreventing reflection by means of the function of the quarter-waveplate; however, a typical quarter-wave plate is effective in preventingreflection only with respect to a particular wavelength in the visiblerange, and unavoidably less effective with respect to wavelengths thatare immediately higher or lower than those particular wavelengths.Further, the brightness of a display is determined by a component of thepolarized light that has travelled through the underlying displaydevice, the component being in a transmission direction of a circularpolarizer that is obtained as a combination of such a quarter-wave platewith a polarizer plate.

More specifically, when the underlying display device has substantiallyno polarization dependence (e.g., a white-Taylar type Guest-Host liquidcrystal display device including dyestuffs added to its 360°-twistedliquid crystal), the reflection efficiency is, at maximum, half that ofa display device having the same arrangement except that no touch panelis provided due to the transmittance of the polarizer plate placed onthe front of the touch panel. Also, as another example, when theunderlying display device utilizes linearly polarized light for adisplay (e.g., a TN or STN type liquid crystal display device includinga polarizer plate further interposed in the space between the touchpanel and the liquid crystal cell), the reflection efficiency is, atmaximum, half that of a display device having the same arrangementexcept that no touch panel is provided. Further, in the last example,since the retardation caused by the quarter-wave plate depends on thewavelength of light, and the quarter-wave plate is sandwiched bypolarizer plates, which causes tonal changes. In either case, brightnessis insufficient, and is not suited for use in a combination with areflective liquid crystal display device to which brightness improvingmeans such as background light cannot be applied.

From what is laid above, it can be said that the touch panel describedin Japanese Laid-Open Patent Application No. 5-127822 needs to beupgraded in its reflection preventing function. Additionally, theLaid-Open Patent Application does not disclose a suitable arrangement toutilize the daylight that has entered the touch panel for the reflectiveliquid crystal display device.

DISCLOSURE OF THE INVENTION

The present invention has objects to solve the aforementioned problemsin a reflective liquid crystal display device of a single polarizerplate mode which can realize a high resolution display, and thereby tooffer a reflective liquid crystal display device that boasts excellentvisibility with a high contrast ratio and a capability to perform acolor display, and to offer, through application of the reflectiveliquid crystal display device, a reflective liquid crystal displaydevice incorporating a touch panel which maintains an enough level ofdisplay quality with a pressure sensitive input device being installed.

To achieve the foregoing objects, a reflective liquid crystal displaydevice in accordance with the invention as defined in this applicationincludes:

a liquid crystal layer sandwiched between a first substrate having alight reflexibility and a second substrate having a lighttransmissibility, the liquid crystal layer being composed oftwist-aligned nematic liquid crystal having a positive dielectricanisotropy; and

circularly polarizing means, including a linear polarizer plate(hereinafter, will be simply referred to as polarizer plate), forselectively passing either right handed or left handed circularlypolarized light out of natural light,

wherein the first substrate, the liquid crystal layer, and thecircularly polarizing means are stacked in this order to form at least apart of the reflective liquid crystal display device,

the circularly polarizing means is disposed so that a major surface ofthe circularly polarizing means is on a liquid crystal layer side, thecircularly polarized light exiting the circularly polarizing meansthrough the major surface when natural light enters the circularlypolarizing means,

the liquid crystal in the liquid crystal layer has a birefringencedifference, which, if multiplied by a thickness of the liquid crystallayer, produces a product of not less than 150 nm and not more than 350nm, and

the liquid crystal layer has a twist angle in a range of 45° to 100°.

The reflective liquid crystal display device is a result of research andefforts by the inventors of the present invention. The inventors of thepresent invention have diligently worked on various reflective liquidcrystal display devices of a single polarizer plate mode which can bearranged to be free from parallax, realize a high resolution display,and be electrically switchable between different polarization states onthe reflector plate required to achieve a bright state and a dark state.As a result, the inventors of the present invention have found that byarranging a reflective liquid crystal display device so as to includecircularly polarizing means and thereby produce a dark state in a statewhere a voltage is applied across the liquid crystal layer, asatisfactory dark state can be achieved without a need for high levelprecision in manufacturing processes of the liquid crystal layer.

The inventors of the present invention have further found that by thusdesigning the liquid crystal layer adopted in a reflective liquidcrystal display device including circularly polarizing means thatproduces such a polarization state and realizes a satisfactory brightstate in a low voltage state, the manufacture of the reflective liquidcrystal display device is facilitated compared to the aforementionedconventional technologies.

In other words, according to the arrangement above, by adopting thecircularly polarizing means and the liquid crystal layer and configuringthe same as stipulated above, problems with conventional arrangementscan be solved and a reflective liquid crystal display device withexcellent display properties can be realized.

In addition, in the reflective liquid crystal display device,preferably, the circularly polarizing means includes: a first opticalretardation compensator plate having a retardation in a substrate normaldirection set to not less than 100 nm and not more than 180 nm; a secondoptical retardation compensator plate having a retardation in asubstrate normal direction set to not less than 200 nm and not more than360 nm; and a linear polarizer plate, the first optical retardationcompensator plate, the second optical retardation compensator plate, andthe linear polarizer plate being stacked in this order when viewed fromthe liquid crystal layer, and |2×θ2−θ1| has a value not less than 35°and not more than 55°, where θ1 represents an angle formed by a slowaxis of the first optical retardation compensator plate and either atransmission axis or an absorption axis of the linear polarizer plate,and θ2 represents an angle formed by a slow axis of the second opticalretardation compensator plate and either the transmission axis or theabsorption axis of the linear polarizer plate.

The inventors of the present invention have found that the preferredarrangement, when incorporated into the polarizer plate and the opticalretardation compensator plate, enables the aforementioned polarizationstate to be obtained by means of the circularly polarizing means. Withthus arranged circularly polarizing means, the light practically in thevisible wavelength range of spectrum can be circularly polarized. Notethat the transmission and absorption axes of the polarizer plate aremutually perpendicular.

In addition, in the reflective liquid crystal display device,preferably, the twist angle of the liquid crystal layer is in a rangefrom 60° to 100°, the product of the birefringence difference of theliquid crystal in the liquid crystal layer and the thickness of theliquid crystal layer is not less than 250 nm and not more than 330 nm,and either the transmission axis or the absorption axis of the polarizerplate forms an angle, θ3, of not less than 20° and not more than 70°, ornot less than 110° and not more than 150° with an alignment direction ofthe liquid crystal molecules in a close proximity of the secondsubstrate.

According to this arrangement, since the product of the birefringencedifference of the liquid crystal in the liquid crystal layer and thethickness of the liquid crystal layer is great, more choices areavailable as materials for the liquid crystal and the thickness of theliquid crystal layer can be easily controlled, facilitating themanufacture of the device. Additionally, by setting θ3 as above, a highquality reflective liquid crystal display device with suppressedcontrast, coloring in a white display, and coloring in a black displaycan be obtained.

In addition, in the reflective liquid crystal display device,preferably, the first substrate having a light reflexibility includes alight reflective film, and the light reflective film has smooth andcontinuously changing concavities and convexities, and is made of aconductive material.

According to the arrangement, a diffuse reflector plate can be obtainedthat causes no unnecessary scattering and has no agitating function(light depolarizing function) to polarized light like a flat specularsurface so as not to interfere with the reflectance modulation methodwhereby the reflective liquid crystal display device carries out a highresolution display. The obtained reflection property is effective byfar, in comparison to a device including a non-diffusive, specularreflector plate and a scattering plate that is installed in front of adisplay device. In addition, since the light reflective film is made ofa conductive material, the light reflective film doubles also as anelectrode to apply voltage across the liquid crystal layer incollaboration with the transparent electrode of the second substrate.

Further, preferably, the concavities and convexities of the lightreflective film have a direction dependent property that variesaccording to a direction on a substrate plane.

The preferred arrangement is a result of our finding that the mean cycleof the concavities and convexities provided on the light reflective filmcharacterize the diffusive reflection property, and more specifically,enables the reflectance of illumination light that travels from aparticular direction and is reflected in a particular direction to beincreased, by uniformly setting the mean convex and concave cycle in anygiven direction on a plane of the reflector plate so that incident lightis uniformly diffused, and modifying the cycle for a particulardirection on the plane. The arrangement is especially effective whenincorporated in a reflective liquid crystal display device in accordancewith the invention as defined in this application which realizes asatisfactory dark state in comparison to Guest-Host mode, enabling evena brighter reflective liquid crystal display device to be obtained.

In addition, in the reflective liquid crystal display device,preferably, a single third optical retardation compensator plate or aplurality of the same is(are) provided between the circularly polarizingmeans and the liquid crystal layer to cancel a residual phase differenceof the liquid crystal layer.

The preferred arrangement is made to eliminate residual phasedifference, i.e., a light polarization modification function, thatslightly remains in accordance with the component of the alignment ofthe liquid crystal that is parallel to the substrate, when the voltageapplied across the liquid crystal layer has limitations and a maximumvoltage is applied across the liquid crystal layer only to achieve adark display. By canceling the residual phase difference by means of thethird optical retardation compensator plate, a satisfactory blackdisplay is achieved at a practically maximum voltage. In addition, thesame effects can be achieved by modifying the retardation of the secondoptical retardation compensator plate.

In addition, in the reflective liquid crystal display device,preferably, either the third optical retardation compensator plate or atleast one of the third optical retardation compensator plates providedbetween the circularly polarizing means and the liquid crystal layer hasan inclined optical axis, or a three-dimensionally aligned optical axishaving therein a continuously varying inclined direction.

In a method to achieve a satisfactory dark display at a maximum value ofan actual driving voltage and hence obtain a satisfactory display,cancelling the residual birefringence of the liquid crystal in a statewhere a substantial voltage is applied across the liquid crystal layeris effective, and to do this, it is possible to expand the viewing angleby expanding a viewing angle range in such a manner to satisfactorilycancel the residual birefringence of the liquid crystal layer.

To achieve this, in this arrangement, either the third opticalretardation compensator plate or at least one of the third opticalretardation compensator plates is designed with the three-dimensionalconfiguration of the alignment of the liquid crystal taken intoconsideration. This enables a reflective liquid crystal display devicehaving more satisfactory display properties to be obtained.

In addition, in the reflective liquid crystal display device,preferably, the first and second optical retardation compensator plateshave such ratios of a refractive index anisotropy, Δn(450), with respectto light having a wavelength of 450 nm, a refractive index anisotropy,Δn(650), with respect to light having a wavelength of 650 nm, and arefractive index anisotropy, Δn(550), with respect to light having awavelength of 550 nm that satisfy

1≦Δn(450)/Δn(550)≦1.06 and

0.95≦Δn(650)/Δn(550)≦1 respectively (the first arrangement), and morepreferably,

1≦Δn(450)/Δn(550)≦1.007 and

0.987≦Δn(650)/Δn(550)≦1 respectively (the second arrangement).

According to the first arrangement, a highly practicable contrast ratioof 10:1 or larger can be achieved although there occur slight coloringin a bright state required of the reflective liquid crystal displaydevice and reduction in contrast due to improvement of the reflectancein a dark state. Further, according to the second arrangement, acontrast ratio of 15:1 or larger can be achieved while successfullyreducing coloring further in comparison to the first arrangement.

In addition, in the reflective liquid crystal display device,preferably, the twist angle of the liquid crystal layer is in a range ofnot less than 65° and not more than 90°, the product of thebirefringence difference of the liquid crystal in the liquid crystallayer and the thickness of the liquid crystal layer is not less than 250nm and not more than 300 nm, and either the transmission axis or theabsorption axis of the polarizer plate forms an angle, θ3, of not lessthan 110° and not more than 150° with an alignment direction of theliquid crystal molecules in a close proximity of the second substrate(in contact with the second substrate).

According to the arrangement, the voltage to drive the liquid crystallayer can be further reduced, and a satisfactory white display can beachieved as well.

In addition, in the reflective liquid crystal display device,preferably, either the transmission axis or the absorption axis of thepolarizer plate forms an angle, θ3, of not less than 110° and not morethan 150° with an alignment direction of the liquid crystal molecules ina close proximity of the second substrate, and a viewing direction isset to a direction on a plane that is defined by a normal to a displaysurface and a direction 90° off the alignment direction of the liquidcrystal molecules in a close proximity of the second substrate.

Similarly, in the reflective liquid crystal display device, preferably,either the transmission axis or the absorption axis of the polarizerplate forms an angle, θ3, of not less than 20° and not more than 70°with an alignment direction of the liquid crystal molecules in a closeproximity of the second substrate, and a viewing direction is set to adirection on a plane that is defined by a normal to a display surfaceand the alignment direction of the liquid crystal molecules in a closeproximity of the second substrate.

According to the arrangement, by thus setting the viewing direction, asatisfactory visibility can be ensured. To put it differently, asatisfactory visibility can be obtained by setting θ3 according to theviewing direction of the viewer. In addition, a satisfactory visibilitycan be obtained also by disposing, for example, a member for setting theviewing direction of the viewer on the display surface.

In addition, in the reflective liquid crystal display device,preferably, either the transmission axis or the absorption axis of thepolarizer plate forms an angle, θ3, of not less than 110° and not morethan 150° with an alignment direction of the liquid crystal molecules ina close proximity of the second substrate, a viewing direction is set toa direction on a plane that is defined by a normal to a display surfaceand a direction 90° off the alignment direction of the liquid crystalmolecules in a close proximity of the second substrate, and the viewingdirection is set to be on a plane that is defined by the normal to thedisplay surface and a direction on a substrate plane in which theconcavities and convexities of the light reflective film have a shortermean cycle than in other directions.

Similarly, in the reflective liquid crystal display device, preferably,either the transmission axis or the absorption axis of the polarizerplate forms an angle, θ3, of not less than 20° and not more than 70°with an alignment direction of the liquid crystal molecules in a closeproximity of the second substrate, a viewing direction is set to adirection on a plane that is defined by a normal to a display surfaceand the alignment direction of the liquid crystal molecules in a closeproximity of the second substrate, and the viewing direction is set tobe on a plane that is defined by the normal to the display surface and adirection on a substrate plane in which the concavities and convexitiesof the light reflective film have a shorter mean cycle than in otherdirections.

According to the arrangement, a particularly excellent visibility can beobtained by further setting the direction in which the light reflectivefilm, that is a diffuse reflector plate, is bright to the satisfactorydirection described above. Note that the direction in which the diffusereflector plate is bright, although being variable typically dependingon the illumination direction and the direction of the viewer, can beaccommodated satisfactorily under a variety of illumination conditions.

In addition, in the reflective liquid crystal display device,preferably, either the transmission axis or the absorption axis of thepolarizer plate forms an angle, θ3, of not less than 40° and not morethan 60° with an alignment direction of the liquid crystal molecules ina close proximity of the second substrate, and the liquid crystalmolecules in a close proximity of the second substrate form an angle θ4with a direction on a plane that is defined by a viewing direction and anormal to a display surface, the angle θ4 being set to not less than 0°and not more than 30°, or not less than 180° and not more than 210°.

According to the arrangement, by thus setting the viewing direction, asatisfactory visibility can be ensured. To put it differently, asatisfactory visibility can be obtained by setting θ3 and θ4 accordingto the viewing direction of the viewer. In addition, a satisfactoryvisibility can be obtained also by disposing, for example, a member forsetting the viewing direction of the viewer on the display surface.

In addition, a reflective liquid crystal display device incorporating atouch panel in accordance with the invention as defined in thisapplication is a reflective liquid crystal display device incorporatinga touch panel that comprises the reflective liquid crystal displaydevice in accordance with the invention wherein a planar pressuresensitive element for detecting an external pressure is sandwiched witha layer-shaped empty space between the circularly polarizing means andthe second substrate.

In the reflective liquid crystal display device in accordance with theinvention as defined in this application, since the light issubstantially circularly polarized after passing the circularlypolarizing means, or the polarizer plate and the two optical retardationcompensator plates, even if the light is reflected at the reflectorplate in such a manner to contain no disturbance in the polarizationstate, the reflected light is absorbed by the polarizer plate beforeexiting the device. Therefore, reflected light does not degradevisibility with a pressure sensitive-type input device (touch panel)that is useful as an input device for a portable device.

Additional objects, advantages and novel features of the invention willbe set forth in part in the description which follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing taken in conjunction with the accompanying drawing or may belearned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically showing a structure of amajor part of a reflective liquid crystal display device of anembodiment in accordance with the present invention.

FIG. 2 is a drawing showing a directional configuration of a polarizerplate and two optical retardation compensator plates of an embodiment.

FIG. 3 is a graph showing a contour drawn by plotting values obtainedfrom calculation of an evaluation function with respect to 550 nmmonochromatic light, the evaluation function being used for predictingthe reflectance of a reflective liquid crystal display device of Example1.

FIG. 4 is a graph showing a contour drawn by plotting values obtainedfrom calculation of an evaluation function taking a visual sensitivityinto consideration, the evaluation function being used for predictingthe reflectance of a reflective liquid crystal display device of Example1.

FIG. 5 is a graph showing a contour drawn by plotting values obtainedfrom calculation of an evaluation function and values of an x-coordinateof CIE1931 standard calorimetric system obtained from calculation of aD₆₅ standard light source spectrum, the evaluation function being usedfor predicting the reflectance of a reflective liquid crystal displaydevice of Example 1.

FIG. 6 is a graph showing a contour drawn by plotting values obtainedfrom calculation of an evaluation function and values of a y-coordinateof CIE1931 standard colorimetric system obtained from calculation of aD₆₅ standard light source spectrum, the evaluation function being usedfor predicting the reflectance of a reflective liquid crystal displaydevice of Example 1.

FIG. 7 is a drawing showing a region where both good white balance andbrightness can be obtained from FIG. 4, FIG. 5, and FIG. 6.

FIG. 8 is a drawing showing a directional configuration of a polarizerplate and two optical retardation compensator plates of a reflectiveliquid crystal display device of Example 3.

FIG. 9 is a drawing showing, in terms of measurements, a voltagedependency of reflectance of the reflective liquid crystal displaydevice of Example 3.

FIG. 10 is a conception drawing showing a configuration of an opticalmeasuring system with which the voltage dependency of reflectance ismeasured on the reflective liquid crystal display device of Example 3.

FIG. 11 is a drawing showing a directional configuration of a polarizerplate and two optical retardation compensator plates of a reflectiveliquid crystal display device of Example 4.

FIG. 12( a) and FIG. 12( b), referring to Samples #5 a and #5 b,respectively, of a reflective liquid crystal display device of Example5, are drawings showing a directional configuration of a polarizerplate, two optical retardation compensator plates, and the alignment ofliquid crystal in a liquid crystal layer.

FIG. 13 is a drawing showing, in terms of measurements, a voltagedependency of reflectance of a reflective liquid crystal display deviceof Example 5.

FIG. 14 is a drawing showing a directional configuration of thealignment of liquid crystal in a close proximity of an upper substrateof Example 7 and a plane that is parallel to a viewing direction.

FIG. 15 is a table showing a result of a visual observation of thereflective liquid crystal display of Example 7 by changing θ4 value.

FIG. 16 is a cross-sectional view schematically showing a structure of amajor part of a reflective liquid crystal display device of Example 8.

FIG. 17 is a drawing showing a directional configuration of a polarizerplate, two optical retardation compensator plates, and the alignment ofliquid crystal in a liquid crystal layer of the reflective liquidcrystal display device of Example 8.

FIG. 18 is an enlarged plan view partially showing concavities andconvexities on a light reflector plate employed in a reflective liquidcrystal display device of Example 9.

FIG. 19 is a conception drawing showing a direction in which thereflection property is measured on a reflective electrode (a lightreflector plate) of Example 9 using an optical measuring system.

FIG. 20 is a drawing showing measurements of the reflection property onthe reflective electrode (the light reflector plate) of Example 9 usingthe measuring system shown in FIG. 19.

FIG. 21( a) through FIG. 21( d), referring to Samples #9 a, #9 b, and #9c, respectively, of the reflective liquid crystal display device ofExample 9, are drawings showing a directional configuration of apolarizer plate, two optical retardation compensator plates, and thealignment of liquid crystal in a liquid crystal layer.

FIG. 22 is a cross-sectional view schematically showing a structure of amajor part of a touch panel employed in a reflective liquid crystaldisplay device incorporating a touch panel of Example 10.

FIG. 23 is a cross-sectional view schematically showing a structure of amajor part of the reflective liquid crystal display device incorporatinga touch panel of Example 10.

FIG. 24 is a cross-sectional view schematically showing a structure of amajor part of the reflective liquid crystal display device incorporatinga touch panel of a comparative example.

FIG. 25 is a cross-sectional view schematically showing a structure of amajor part of the reflective liquid crystal display device of anotherembodiment in accordance with the present invention.

FIG. 26 is a drawing showing a directional configuration of a polarizerplate and two optical retardation compensator plates of anotherembodiment.

FIG. 27 is an explanatory drawing showing voltage inducing differentstates of the alignment of a liquid crystal layer of a reflective liquidcrystal display device.

FIG. 28 is an explanatory drawing showing changes in the viewing anglecharacteristic with a relationship between the direction of illuminationand that of the alignment of a liquid crystal layer of a reflectiveliquid crystal display device.

FIG. 29 is a drawing showing, in terms of measurements, a voltagedependency of reflectance of a reflective liquid crystal display deviceof Example 11.

FIG. 30 is a cross-sectional view showing a structure of a major part ofSample #12 a of Example 12.

FIG. 31 is a cross-sectional view showing a structure of a major part ofSample #12 b of Example 12.

BEST MODES FOR CARRYING OUT THE INVENTION

Referring to examples and embodiments, the following description willdiscuss the present invention in far more detail and the presentinvention is by no means limited by the discussion.

First Embodiment of the Invention

Referring to drawings, the following description will discuss anembodiment in accordance with the present invention.

FIG. 1 is a cross-sectional view schematically showing a structure of amajor part of a reflective liquid crystal display device of an examplein accordance with the present invention. As can be seen from FIG. 1,the reflective liquid crystal display device includes a liquid crystallayer 1 that contains twisted nematic liquid crystal having a positivedielectric anisotropy, sandwiched between a substrate 4 on which analignment-processed alignment layer 2 is formed and a substrate 5 onwhich a similarly alignment-processed alignment layer 3 is formed.Further, on the lower substrate 5, there is disposed a light reflectivefilm 7; preferably, the reflecting surface of the light reflective film7 has such smooth concavities and convexities that preserve thepolarization throughout the reflection of light. More preferably, thesmooth concavities and convexities are such that the concavity andconvexity cycle varies according to the azimuth direction on thereflecting surface of the light reflective film 7.

On the upper substrate 4, there is provided a transparent electrode 6.The light reflective film 7 on the lower substrate 5 is formed from aconductive material and doubles as an electrode. Voltage is appliedacross the liquid crystal layer 1 through the transparent electrode 6and the light reflective film 7. As means for applying a voltage to thethus arranged electrode pair, an active switching element may be used;however, there are no limitations in particular. Note that if a memberthat does not serve as an electrode is employed as the light reflectivefilm 7, an electrode should be provided to the side on which thesubstrate 5 is disposed.

Further, on a display surface of the liquid crystal drive cell thusarranged from the substrates 4 and 5 and the liquid crystal layer 1, thedisplay surface being on the side where the substrate 4 is disposed,there is provided circularly polarizing means 100 for filtering naturallight and selectively passing either right handed or left handedcircularly polarized light. In the present example, the circularlypolarizing means 100 is constituted by an optical retardationcompensator plate 8, an optical retardation compensator plate 9, and apolarizer plate 10 stacked in this sequence on the display surface onthe side where the substrate 4 is disposed side.

The following description will discuss optical properties and functionsof these optical elements, i.e., the optical retardation compensatorplate 8, the optical retardation compensator plate 9, and the polarizerplate 10.

The reflective liquid crystal display device of the present embodimentallows illumination light, such as external light, to enter the liquidcrystal layer 1 through the polarizer plate 10, and is viewed from theside of the polarizer plate 10 through which the illumination lightenters. The polarizer plate 10 selectively passes only a linearlypolarized light component in a particular direction, and the opticalretardation compensator plate 9 and the optical retardation compensatorplate 8 change the polarization state of the incoming linearly polarizedlight component.

Here, the incoming light, after having passed through the opticalretardation compensator plate 8, is substantially circularly polarizedunder the conditions that the retardation is not smaller than 100 nm andnot greater than 180 nm in the substrate normal direction of the opticalretardation compensator plate 8 and not smaller than 200 nm and notgreater than 360 nm in the substrate normal direction of the opticalretardation compensator plate 9, and the value of |2×θ2−θ1| is notsmaller than 35° and not larger than 55°, where θ1 is the angle formedby the slow axis of the optical retardation compensator plate 8 andeither the transmission axis or the absorption axis of the polarizerplate 10 and θ2 is the angle formed by the slow axis of the secondoptical retardation compensator plate 9 and either the transmission axisor the absorption axis of the polarizer plate 10. In such an event,whether the light in circularly polarization is right handed or lefthanded depends on the configuration of these three optical elements(i.e., the optical retardation compensator plate 8, the opticalretardation compensator plate 9, and the polarizer plate 10).

To further illustrate this, a detailed description will be given belowby reference to FIG. 2 which shows a configuration example. It should benoted, however, that in this example the reflective liquid crystaldisplay device is viewed from the direction in which light enters.Incident light, which enters the liquid crystal display device, passesthrough the polarizer plate 10, the optical retardation compensatorplate 9, and the optical retardation compensator plate 8, and thereforebecomes substantially right handed circularly polarization, if the threeoptical elements are configured as shown in FIG. 2, or morespecifically, if the three optical elements are configured so as tosatisfy θ1=75° and θ2=15°, where 11 represents the transmission axis ofthe polarizer plate 10, 13 represents the slow axis of the opticalretardation compensator plate 8, 12 represents the slow axis of theoptical retardation compensator plate 9, θ1 represents the angle formedby the transmission axis 11 of the polarizer plate 10 and the slow axis13 of the optical retardation compensator plate 8, and θ2 represents theangle formed by the transmission axis 11 of the polarizer plate 10 andthe slow axis 12 of the optical retardation compensator plate 9.

Further, the incident light, which enters the liquid crystal layer 1,changes its polarization state by means of a polarized light conversionfunction of a twisted birefringent medium (liquid crystal) in the liquidcrystal layer 1 that aligns according to an applied voltage, and reachesthe reflector plate. In such an event, the polarization state on thelight reflective film 7 varies depending on the alignment of the liquidcrystal molecules.

First, the dark state will be explained. If the liquid crystalmolecules, upon the application of voltage, align parallel to thegradient direction of the applied voltage, and has no polarized lightconversion function on the light travelling parallel to the normal tothe device, the incoming circularly polarized light reaches the lightreflective film 7 while allowing no changes in the polarization thereof,and a dark state is achieved. By establishing a dark state across thewhole visible range, a black display is achieved.

The inventors of the present invention have found that to prepare apolarization state similar to this one virtually across the visiblerange, the following conditions need to be fulfilled. The opticalretardation compensator plate 8 needs to have such a property to providethe light in the main visible range of 400 nm to 700 nm with a phasedifference that is equivalent to a quarter wavelength, e.g., to providethe light having a wavelength of 550 nm with a retardation of 100 nm to180 nm. Further, the optical retardation compensator plate 9 needs tohave such a property to provide the light in the same main visible rangewith a phase difference that is equivalent to half the wavelength, e.g.,to provide the light having a wavelength of 550 nm with a retardation of200 nm to 360 nm.

Further, according to the configuration of the polarizer plate 10 andthe optical retardation compensator plates 8 and 9 shown in FIG. 2,since θ1=75° and θ2=15° as mentioned earlier, |2×θ2−θ1|=45°, and thefollowing equation is satisfied:35°≦|2×θ2−θ1|≦55°  (1)

Although obviously the values of θ1 and θ2 may be changed as long asthis equation is satisfied, the specific values are preferablydetermined by a combination of dispersion of the birefringence of thetwo optical retardation compensator plates 8 and 9 used. In addition,the value of |2×θ2−θ1| may vary in a 20° range according to the anglesetting stipulated in Equation (1), and the preferable value within thisrange further varies depending on the polarized light conversionfunction of the liquid crystal layer 1 in a case where a voltage isapplied across the liquid crystal layer 1. In other words, theconfiguration is preferably specified so that light is circularlypolarized on the light reflective film 7 while taking birefringence atthe optical retardation compensator plates 8 and 9 and the liquidcrystal layer 1 into consideration. In such an event, the polarizedlight conversion function of the liquid crystal layer 1, when a voltageis substantially applied across the liquid crystal layer 1, does notcritically depend on precision in the manufacture of the liquid crystallayer 1, the liquid crystal layer 1 can be thereby easily fabricated andmanufactured.

Next, the function of the bright state will be explained. A bright statecan be achieved by altering the substantially circularly polarizedincident light into a linearly polarized light on the light reflectivefilm 7 with the optical retardation compensator plates 8 and 9 that areconfigured so as to fulfill aforementioned Equation (1). In other words,irrespective of whether the light having wavelengths in the visible areais linearly polarized in directions that vary depending on thewavelengths or linearly polarized light in the same directionirrespective of the wavelengths, a similarly bright state can beachieved.

This renders it important to realize a liquid crystal layer 1 havingsuch an optical function that the incoming light to the liquid crystallayer 1, which is substantially circularly polarized to realize theaforementioned dark state, becomes polarized linearly in arbitrarydirections in a visible wavelength range.

Taking the electric drive which facilitates the fabrication andmanufacture of the liquid crystal layer 1 into consideration, since thedark state is achieved in a voltage applied state, the bright stateneeds to be realized either in a non-voltage applied state or in a statewhere the alignment of the liquid crystal molecules changes withvoltage, however, in a greatly different manner from the changes in adark state.

The inventors of the present invention have diligently worked andsuccessfully found a range across which to realize a practicallysufficient function of a bright state, in other words, a range acrosswhich to ensure sufficient brightness in the visible range of spectrumand to enable development of liquid crystal composition that is suitableto liquid crystal display devices that can be readily manufactured withhigh yields.

Specific conditions to achieve that is to set the twist angle of thetwisted nematic liquid crystal in the liquid crystal layer 1 to notsmaller than 45° and not greater than 100°, and to set the product, Δnd,of the birefringence difference Δn of the liquid crystal in the liquidcrystal layer 1 and the thickness d of the liquid crystal layer 1 to notsmaller than 150 nm and not greater than 350 nm.

Here, more preferably, the twist angle is set to not smaller than 60°and not greater than 100°, and the product, Δnd, of the birefringencedifference Δn of the liquid crystal in the liquid crystal layer 1 andthe thickness d of the liquid crystal layer 1 to not smaller than 250 nmand not greater than 300 nm. Even more preferably, the twist angle isset to not smaller than 65° and not greater than 90°, and the product,Δnd, of the birefringence difference Δn of the liquid crystal in theliquid crystal layer 1 and the thickness d of the liquid crystal layer 1to not smaller than 250 nm and not greater than 300 nm. Even under sucha condition in fabrication of the liquid crystal display device that thethickness of the liquid crystal layer 1 is set to 4.5 μm for example,the even more preferable range conditions can be fulfilled with apractical liquid crystal material that includes a liquid crystal layer 1of which Δn is approximately 0.0667, allowing a highly practical liquidcrystal display device to be manufactured.

Specific examples will be discussed in the following in accordance withthe present embodiment.

EXAMPLE 1

First, as Example 1, the description below will explain an evaluation ofspecifications of the liquid crystal layer by means of calculation, thatare required to specifically design the liquid crystal layer with theoptical functions thereof being taken into consideration. For optimumdesign of the liquid crystal layer, the evaluation function given byEquation (2) is used to evaluate specifications of the liquid crystallayer:f=1−s ₃ ²  (2)

Here, s₃ is a Stokes parameter to specify a polarization state, morespecifically, a Stokes parameter regarding the polarization state of thelight that has passed through the liquid crystal layer only once on thereflecting surface. Note that the Stokes parameter used here isnormalized.

When the intensity of light is normalized, the polarization state of theperfectly polarized light of which the polarization state can bedescribed by a Stokes parameter having three components: s₁ and s₂represent the respective linearly polarized light components of whichthe vibration surfaces differ from each other by 45°, while s₃ denotesthe circularly polarized light component. s₁, s₂, s₃ are not less than−1 and not more than 1: among them, s₃ equals ±1 for circularlypolarized light, 0 for linearly polarized light, and a value betweenthese two values for elliptically polarized light.

In other words, the evaluation function f produces three valuesaccording to the polarization state on the reflecting surface: f=0 forcircularly polarized light, 0<f<1 for elliptically polarized light, andf=1 for linearly polarized light, irrespective of the handedness ofpolarized light as a result of the squaring of s₃.

It has been confirmed by an analysis conducted by the inventors of thepresent invention that supposing that light enters, any givenbirefringence medium sandwiched between a single polarizer plate and areflecting surface that reflects as a specular surface from thepolarizer plate side, the reflected light is completely absorbed by thepolarizer plate through which the light has passed upon entering in thecase of f=0 (circularly polarized light) on the reflector plate, and canpass through the polarizer plate without being absorbed in the case off=1. When the evaluation function f produces a value between these twovalues, the reflected light is partially absorbed by the polarizerplate, and the rest of the reflected light passes through the polarizerplate, resulting in a display with an intermediate reflectance.

Further, it has been found that the evaluation function f is directlyproportional to the reflectance of such a reflective liquid crystaldisplay device with a single polarizer plate that reflects incidentlight at the reflector plate, and that the reflectance of the singlepolarizer plate mode can be evaluated. Therefore, by using theevaluation function f, it is possible to predict both whether or notsatisfactory brightness can be obtained in the bright display andwhether or not a satisfactory dark state can be obtained.

As seen from the above, the evaluation function f can be used to predictdisplay performance, and the inventors of the present invention haveworked to find a liquid crystal display mode whereby the singlepolarizer plate mode is expected to show best performance. A specificscheme will be explained in the description below.

First, a consideration is given to mass productivity in the fabricationof liquid crystal display devices. A special attention is paid tomaintaining precision of the thickness of the liquid crystal layer,because the thickness determines optical properties of the liquidcrystal display device and the maintenance of precision greatly affectsproductivity.

As a method of maintaining the thickness of the liquid crystal layer, amethod of providing spherical spacers fabricated to have a singlediameter and disposed between the substrates sandwiching the liquidcrystal layer would result in an excellent balance between precision andpractical performance. However, even with this method being employed,requirement for high precision in mass production leads to a rise inmass production costs. As can be understood from this, it is importantfor industrial purposes to develop a method that does not requireprecision in the thickness of the liquid crystal layer.

It is also important to consider characteristics of human visual sensewith respect to display quality of the fabricated liquid crystal displaydevice. It is known regarding human visual sense that the perceivedbrightness is not in direct proportion to the actual intensity of lightthat stimulates the retina of an eyeball, but rather shows a non-linearcharacteristic. More specifically, the same variations in the lightintensity from a display device feels like a small variation inbrightness (when the background presents a strong stimulation) or agreat variation in brightness (when the background presents a weakstimulation), depending on the strength of stimulation presentedsimultaneously to the retina. With the non-linear characteristic ofvisual sense being taken in consideration, it would be understood thatthe same level of irregularity in reflectance could degrade displayquality further when that happens to a dark display than to a brightdisplay.

As can be understood from the above description, if there exist twostates, one with a relatively large irregularity in reflectance and theother with a relatively small irregularity in reflectance, the statewith a relatively small irregularity in reflectance is preferablyassigned to dark display, and the state with a relatively largeirregularity in reflectance to bright display, so as to enable thefabrication of liquid crystal display elements of satisfactory displayquality.

Further, when the polarized light conversion function is lost byapplying a substantial voltage across the liquid crystal layer,irregularity in thickness of the liquid crystal layer is less likely toresult in a great variation in the polarized light conversion function.

Taking the above three items above, it could be understood thatsatisfactory display can be achieved by assigning, to dark display, analignment state wherein a substantial voltage is applied. In otherwords, it is preferable to assign, to bright display, a state wherein novoltage is applied across the liquid crystal, and also to assign, todark display, a state wherein a voltage is applied across the liquidcrystal, that is, to adopt a so-called normally white operations.

Next, on the basis of the evaluation function f, the description belowwill explain the specifications of optical retardation compensator plateand of the liquid crystal layer portion to realize these specifications.

First, in a case where a substantial voltage is applied across theliquid crystal layer, the liquid crystal layer does not have a polarizedlight conversion function. The optical retardation compensator plate isrequired to have a property to change light so that light has passedthrough the liquid crystal layer and reached the reflector plate tobecome circularly polarized light on the reflector plate. Here, thehandedness of the circularly polarized light is either right handed orleft handed.

The aforementioned specifications regarding the optical retardationcompensator plate enables this property to be obtained across a wideband of spectrum. In such an event, since the polarized light conversionfunction of the liquid crystal has been lost, the evaluation function fequals 0 and a satisfactory dark state occurs.

In contrast, in a case where no voltage is applied across the liquidcrystal layer, in order to examine conditions to obtain sufficientreflective brightness, it is necessary to evaluate the evaluationfunction f with the optical retardation compensator plate specified asabove to produce circularly polarized light. The inventors of thepresent invention have obtained an evaluation function f for such analignment that the liquid crystal layer is uniformly twisted, in a statewhere no voltage is applied across the liquid crystal layer. As aresult, it has been found, from analytic calculation of s₃ using JonesMatrix method, that when circularly polarized light enters the liquidcrystal, the evaluation function f is given by Equation (3).

$\begin{matrix}\begin{matrix}{f = {1 - \left\{ {1 - {2{\phi_{ret}^{2}\left( {{sinc}\sqrt{\phi_{ret}^{2} + \phi_{tw}^{2}}} \right)}^{2}}} \right\}^{2}}} \\{\phi_{ret} = {\pi\frac{\Delta\;{nd}}{\lambda}}} \\{{{sinc}\; X} = \frac{\sin\; X}{X}}\end{matrix} & (3)\end{matrix}$φ_(tw): Twist angle between the upper and lower substrates

FIG. 3 shows, as a contour plot, values of the evaluation function f ata wavelength that produces the highest visual sensitivity (λ=550 nm)against Δnd and the twist angle of the liquid crystal layer, which aredesign parameters thereof. Note that since the function f is an evenfunction, values of the function f are shown only for positive values ofthe twist angle φ_(tw); however, needless to say, the actual twistdirection of the alignment of the liquid crystal may be either righthanded or left handed.

FIG. 3 only shows values for a single wavelength (550 nm). The samemethod of evaluation can be used for wavelengths in a visible range,i.e., from 380 nm to 780 nm. The application of the method to incidentlight having wavelengths other than 550 nm only requires changes in Δnand λ among other variables of the evaluation function f.

The consideration of effects on human vision that vary depending on thewavelength as detailed above and the calculation of an overlappingintegral with the function fon assumptions of the visual sensitivity anda standard illumination light source enables more precise optimization.Specifically, it is useful to substitute the visual sensitivity curve(y_(BAR)(λ) of the color matching function of CIE1931) and the spectrumdensity S_(D65)(λ) of a D₆₅ standard light source into aforementionedEquation (3), and to define it as Equation (4).

$\begin{matrix}{{f_{vis} = {k{\int_{380}^{780}{{\overset{\_}{y}(\lambda)}{S_{D65}(\lambda)}{f(\lambda)}\ {\mathbb{d}\lambda}}}}}{k = {1/{\int_{380}^{780}{{\overset{\_}{y}(\lambda)}{S_{D65}(\lambda)}\ {\mathbb{d}\lambda}}}}}} & (4)\end{matrix}$

Here, f(λ), being obtained from calculation of Equation (3), clearlyshows that the function is dependent to the wavelength λ.

Thus defined f_(vis) is calculated for Δnd and the twist angle in thesame manner as in FIG. 3, and shown in FIG. 4. Here, the calculation isdone taking the dispersion of Δn into consideration, and Δnd on the axisof ordinates shows values for the light having a wavelength of 550 nm.

Further, since the evaluation function f given by Equation (2) showsvalues that are in direct proportion to the reflectance of a display, bychanging the color matching function y_(BAR) (λ) of Equation (4) tox_(BAR) (λ) or z_(BAR) (λ) that are similarly specified in CIE1931, itbecomes possible to calculate chromaticity. Hence, the chromaticity (x,y) at the D₆₅ light source is calculated for the same parameters as inFIG. 4. The resultant x and y values are shown in FIGS. 5 and 6respectively.

With all these taken into consideration, conditions are specified toproduce a sufficient luminous reflectance (f_(vis) is 0.7 or higher) andsatisfactory hue in a white display (x is not less than 0.27 and notmore than 0.35, and y is not less than 0.28 and not more than 0.36), anda suitable Δnd and range of twist color are obtained. Results are shownin FIG. 7.

In this manner, the ranges of parameters of a liquid crystal layer areobtained which are required to realize sufficient brightness and hue.However, the specifications of the liquid crystal layer further includea limitation as a result of specification of the thickness of the liquidcrystal layer of the liquid crystal material. Therefore, not every partof the hatched range in FIG. 7 would be suitable for practical purposes.In addition, satisfactory conditions can be found slightly out of therange too. A further description will be given regarding this.

It is known that an optical property, Δn, of the liquid crystal materialand a temperature range in which the liquid crystal material functionsproperly has a certain correlation. Specifically, the liquid crystalmaterial for actual use, typically being adjusted to have necessaryproperties by blending with some compositions, will have a narrowertemperature range to obtain nematic phase when Δn decreases as a resultof a change in the blend ratio. In such a case, it is difficult todramatically narrow the operational and preservable temperature rangesof the liquid crystal display device. That is, in view of thetemperature range to stably obtain a nematic phase, Δn of the liquidcrystal material has a lower limit. For these reasons, Δn at roomtemperature, although depending on necessary temperature range, etc., isrequired to be approximately not less than 0.05, preferably not lessthan 0.065.

In addition, the thickness of the liquid crystal layer has limitationsdue to the rate of defective products that are caused during thefabrication process of the liquid crystal display device by undesirabledust and the like, and also due to level differences in fabricatingelements for driving the liquid crystal, flatness of the substrate used,etc. Further, when the liquid crystal layer is adopted in a part of anarrangement in accordance with the invention as defined in thisapplication, the concavities and convexities of a concave and convexdiffuse reflector plate that is located near the liquid crystal layeradds to the limitations.

For transmissive liquid crystal display devices, the thickness of theliquid crystal layer is set to approximately 5 μm and manufacturingtechnology has been well established for such an arrangement. Todramatically reduce the thickness of the liquid crystal layer furtherwould be extremely difficult and not practical. Therefore, the liquidcrystal layer should be fabricated so as to have a thickness ofapproximately not less than 3 μm, preferably not less than 4 μm.

From those viewpoints laid out above, it is useful to set Δnd, that isthe product of the refractive index difference, Δn, of the liquidcrystal and the thickness, d, of the liquid crystal layer, to not lessthan 150 nm, preferably to not less than 260 nm.

Further, in actual liquid crystal of a liquid crystal display devicewhich is in a driven state, a voltage that is more than a closeproximity of the threshold value of the liquid crystal which showsthreshold value characteristics is applied for driving the liquidcrystal in many cases. In such an event, the liquid crystal, acrosswhich a voltage near the threshold value is applied, somewhat inclinesin comparison to the state where no voltage is applied, and therefractive index difference in the substrate normal direction in thesomewhat inclining state appears in an actual display.

As can be understood from this, Δn determined by the liquid crystalmaterial may take a value approximately 10% larger than effective Δnwith respect to the inclined liquid crystal. Note that since it ispossible to carry out a display at the threshold value or lower of theliquid crystal, appropriately this change in the value of Δnd is notapplied to the lower limit of Δnd.

As detailed above, the inventors of the present invention have foundthat from the specific calculation using actual specifications of theliquid crystal layer, it is useful in the reflective liquid crystaldisplay device in the single polarizer plate mode to set Δnd to not lessthan 150 nm, with 350 nm being the upper limit thereof, and to set thetwist angle of the liquid crystal to 45° to 100°.

[Example 2]

In Example 2, reflective liquid crystal display devices structured as inaforementioned FIG. 1 were fabricated with parameters listed in table 1to obtain five Samples #2 a through #2 f.

TABLE 1 Sample Parameter #2a #2b #2c #2d #2e #2f Δnd 260 330 120 380 260260 θ3 (°) 40 40 40 40 55 20 Twist Angle (°) 70 70 70 70 40 110 θ1 (°)75 75 75 75 75 75 Retardation Caused 135 135 135 135 135 135 by OpticalRetardation Compensator Plate 8 θ2 (°) 15 15 15 15 15 15 RetardationCaused 270 270 270 270 270 270 by Optical Retardation Compensator Plate9

Display results of Samples are shown roughly in Table 2.

TABLE 2 Sample Voltage #2a #2b #2c #2d #2e #2f 0 White Yellowish GrayOrangish Reddish Gray Display White White White Display Display DisplayVth White White Gray Yellowish Yellowish Gray Display Display WhiteWhite Display Display 1.5 × Vth Gray Gray Dark White White Dark GrayDisplay Display Gray 2.0 × Vth Dark Dark Gray Dark Gray Gray Black GrayGray 3.0 × Vth Black Black Black Dark Gray Dark Gray Black

Note that Vth refers to threshold voltage values where change in thealignment of the liquid crystal layer 1 is observed with each sample,and takes different values due to Δnd that is set to different values.

As shown in the above, as for Samples #2 a and #2 b whose parametersfell in the range of the reflective liquid crystal display device inaccordance with the present invention, a white display changed into ablack display when the voltage changed from the actually used voltage,i.e., Vth to 3.0×Vth. In contrast, as for Samples #2 c through #2 fwhose parameters did not fall in the range of the reflective liquidcrystal display device in accordance with the present invention, thedisplay was dark (Samples #2 c and #2 f), or colored (Samples #2 d and#2 e).

Those display results shown in Table 2 show that such large changes inproperties that happened to Samples #2 a through #2 f were not observedif only the specified relative angle, θ3, formed with the alignmentdirection of the liquid crystal is changed without changing the relativeangles, θ1 and θ2, between the polarizer plate 10 and the opticalretardation compensator plates 8 and 9, and confirm rather thedependency on the specifications of the liquid crystal layer 1.

In addition, similar displays as shown in Table 2 were observed with allcombinations: for example, such specifications that the light polarizedcircularly in reverse handedness enters the liquid crystal (i.e., θ1 andθ2 simultaneously increased by 90°, or both θ1 and θ2 altered in sign)and such specifications to obtain the light polarized circularly in thesame direction (i.e., both θ1 and θ2 changed in sign and increased by90°).

The above description shows that by specifying the liquid crystal layer1 so that the product of the birefringence difference of the liquidcrystal in the liquid crystal layer 1 and the thickness of the liquidcrystal layer is not less than 150 nm and not more than 350 nm, and thetwist angle of the liquid crystal layer is in a range of 45° to 100°, asatisfactory display can be realized in the limited range.

Following Examples 3 and 4 show optimization examples in which theinventors of the present invention examined conditions to achieve moresatisfactory display.

EXAMPLE 3

As Example 3, a reflective liquid crystal display device will bedescribed that includes a liquid crystal layer of which the twist angleof the twisted nematic liquid crystal is set to 90° and two opticalretardation compensator plates have retardation of 135 nm and 270 nmrespectively.

In Example 3, a reflective liquid crystal display device structured asshown in aforementioned FIG. 1 was fabricated. The light reflective film7 on a substrate 5 was made of aluminum and served as a light reflectiveelectrode. In addition, the liquid crystal drive cell was a 90° twistedliquid crystal layer 1 that was adjusted to have a thickness of 4.2 μmafter the introduction of liquid crystal, the introduced liquid crystalmaterial used here having the same liquid crystal physical properties(dielectric anisotropy, elasticity, viscosity, nematic temperaturerange, and voltage retaining property) as the liquid crystal used in atypical TFT transmissive liquid crystal display device only except Δnwhich was adjusted to 0.065. Here, the product of the thickness of theliquid crystal layer 1 and the birefringence difference of the liquidcrystal was set to 273 nm.

In the present example, the polarizer plate 10, the optical retardationcompensator plate 8, and the optical retardation compensator plate 9were configured as shown in FIG. 8. Note in FIG. 8 that 11 refers to thetransmission axis direction of the polarizer plate 10, 12 refers to theslow axis direction of the optical retardation compensator plate 9, 13refers to the slow axis direction of the optical retardation compensatorplate 8, 14 refers to the direction of the alignment of the liquidcrystal molecules that are in contact with the alignment layer 2 formedon a substrate 4, i.e., that are in a close proximity of the alignmentlayer 2, and 15 refers to the direction of the alignment of the liquidcrystal molecules that are in contact with the alignment layer 3 formedon a substrate 5, i.e., that are in a close proximity of the alignmentlayer 3, and also that the figure is viewed from the direction of theincident light on the liquid crystal display device.

Further, the positional relationship, as shown in FIG. 8, stipulatesthat the angle, θ1, formed by the transmission axis direction 11 of thepolarizer plate 10 and the slow axis direction 13 of the opticalretardation compensator plate 8 was set to 75°, the angle, θ2, formed bythe transmission axis direction 11 of the polarizer plate 10 and theslow axis direction 12 of the optical retardation compensator plate 9was set to 15°, and the angle, θ3, formed by the alignment direction 14of the liquid crystal molecules on the substrate 4 and the transmissionaxis direction 11 of the polarizer plate 10 was set to 30°.

The optical retardation compensator plate 8 and the optical retardationcompensator plate 9 were both formed from an oriented film made ofpolyvinylalcohol; the optical retardation compensator plate 8 introduceda phase difference controlled to 130 nm to 140 nm to the light having awavelength of 550 nm that traveled therethrough in a normal direction,and the optical retardation compensator plate 9 introduced a phasedifference controlled to 265 nm to 275 nm to the same kind of light.

The optical retardation compensator plates 8 and 9 were configured insuch a manner to enhance the optical properties of the fabricated liquidcrystal display device in the front direction; however, theirconfiguration, including the liquid crystal layer 1, may be changedwhile considering characteristics in observation from an obliquedirection. For example, either or each of the optical retardationcompensator plates 8 and 9 may be replaced with a biaxial opticalretardation compensator plate, so as to alter the phase differencesintroduced to the light passing in an oblique direction by the opticalretardation compensator plates 8 and 9 while satisfying conditions onthe settings of the angles in accordance with the present example asshown in FIG. 8. In addition, needless to say, the settings of theangles may be altered within the range given by aforementioned Equation(1).

Further, as the polarizer plate 10, a polarizer plate was used thatincluded an AR layer made up of multi-layered dielectric films andshowed a transmittance of 45% when measured in a single piece.

A graph is shown in FIG. 9 illustrating a voltage dependency ofreflectance of the reflective liquid crystal display device arranged inthe aforementioned manner. The reflectance was measured, as shown inFIG. 10, in a driven state where voltage was applied across thereflective liquid crystal display device in accordance with the presentexample, using an optical detector detecting the light that radiatedfrom an illumination light source device, travelled via a half mirror toenter on the side where the substrate 4 is disposed, and reflected atthe light reflective film disposed on a substrate 5. Further, in FIG. 9,the reflectance at 100% represents a measurement on the same liquidcrystal display device as that of the present example, except that itincludes no optical retardation compensator plates, but only the samepolarizer plates as those in the device on which measurement isconducted as above, in a state where liquid crystal is not filled. Inaddition, luminous reflectance (Y values) is employed as thereflectance.

As can be seen from the measurement results shown in FIG. 9, a highreflectance was obtained at a drive voltage as low as about 1V or evenlower.

EXAMPLE 4

As Example 4, a reflective liquid crystal display device will bedescribed that includes a liquid crystal layer of which the twist angleof the twisted nematic liquid crystal is set to 70° and two opticalretardation compensator plates have retardation of 135 nm and 270 nmrespectively.

In Example 4, a reflective liquid crystal display device structured asshown in aforementioned FIG. 1 was fabricated. The light reflective film7 on a substrate 5 was made of aluminum and served as a light reflectiveelectrode. In addition, the liquid crystal drive cell was a 70° twistedliquid crystal layer 1 that was adjusted to have a thickness of 4.5 μm(Sample #4 a) or 4.2 μm (Sample #4 b) after the introduction of liquidcrystal, the introduced liquid crystal material used here having thesame liquid crystal physical properties (dielectric anisotropy,elasticity, viscosity, nematic temperature range, and voltage retainingproperty) as the liquid crystal used in a typical TFT transmissiveliquid crystal display device only except Δn which was adjusted to 0.06.Here, the product of the thickness of the liquid crystal layer 1 and thebirefringence difference of the liquid crystal was set to 270 nm (Sample#4 a) or 250 nm (Sample #4 b).

In the present example, the polarizer plate 10, the optical retardationcompensator plate 8, and the optical retardation compensator plate 9were configured as shown in FIG. 11. Note in FIG. 11 that 11 refers tothe transmission axis direction of the polarizer plate, 12 refers to theslow axis direction of the optical retardation compensator plate 9, 13refers to the slow axis direction of the optical retardation compensatorplate 8, 14 refers to the direction of the alignment of the liquidcrystal molecules that are in contact with the alignment layer 2 formedon a substrate 4, i.e., that are in a close proximity of the alignmentlayer 2, and 15 refers to the direction of the alignment of the liquidcrystal molecules that are in contact with the alignment layer 3 formedon a substrate 5, i.e., that are in a close proximity of the alignmentlayer 3, and also that the figure is viewed from the direction of theincident light on the liquid crystal display device.

Further, the positional relationship, as shown in FIG. 11, stipulatesthat the angle, θ1, formed by the transmission axis direction 11 of thepolarizer plate 10 and the slow axis direction 13 of the opticalretardation compensator plate 8 was set to 75°, the angle, θ2, formed bythe transmission axis direction 11 of the polarizer plate 10 and theslow axis direction 12 of the optical retardation compensator plate 9was set to 15°, and the angle, θ3, formed by the alignment direction 14of the liquid crystal molecules on the substrate 4 and the transmissionaxis direction 11 of the polarizer plate 10 was set to 45°.

The optical retardation compensator plate 8 and the optical retardationcompensator plate 9 were both formed from an oriented film made ofpolyvinylalcohol; the optical retardation compensator plate 8 introduceda phase difference controlled to 130 nm to 140 nm to the light having awavelength of 550 nm that travelled therethrough in a normal direction,and the optical retardation compensator plate 9 introduced a phasedifference controlled to 265 nm to 275 nm to the same kind of light.

The optical retardation compensator plates 8 and 9 were configured insuch a manner to enhance the optical properties of the fabricated liquidcrystal display device in the front direction; however, theirconfiguration, including the liquid crystal layer 1, may be changedwhile considering characteristics in observation from an obliquedirection. For example, either or each of the optical retardationcompensator plates 8 and 9 may be replaced with a biaxial opticalretardation compensator plate, so as to alter the phase differencesintroduced to the light passing in an oblique direction by the opticalretardation compensator plates 8 and 9 while satisfying conditions onthe settings of the angles in accordance with the present example asshown in FIG. 11. In addition, needless to say, the settings of theangles may be altered within the range given by aforementioned Equation(1).

Further, as the polarizer plate 10, a polarizer plate was used thatincluded an AR layer made up of multi-layered dielectric films andshowed a transmittance of 45% when measured in a single piece.

The reflectance of the reflective liquid crystal display device arrangedin the aforementioned manner showed the same voltage dependency as thatillustrated in the graph in aforementioned FIG. 9. As can be seen fromthese results, a high reflectance was obtained at a drive voltage as lowas about 1V or even lower. Note that the reflectance was measured, shownin FIG. 10, using the same optical measuring system as in aforementionedExample 3 and also that the reflectance at 100% was set in the samemanner as in aforementioned Example 3.

In addition, Table 3 shows contrast, coloring in white, and coloring inblack for a variety of angles, θ3, formed by the transmission axis ofthe polarizer plate 10 and the alignment direction of the liquid crystalin a close proximity of the upper substrate 4.

TABLE 3 Sample #4a Sample #4b θ3/ Coloring Coloring Overall ColoringColoring Overall degree Contrast In White In Black Evaluation ContrastIn White In Black Evaluation 0 x x x x Δ Δ x x 10 Δ Δ x x ∘ ∘ x x 20 Δ ΔΔ Δ ∘ ∘ Δ Δ 30 Δ Δ ∘ Δ ∘ ∘ ∘ ∘ 40 ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 50 ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 60∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 70 ∘ ∘ Δ Δ ∘ ∘ Δ Δ 80 ∘ ∘ x x ∘ ∘ x x 90 ∘ ∘ x x ∘ ∘ x x100 Δ Δ x x ∘ ∘ x x 110 Δ Δ Δ Δ ∘ ∘ Δ Δ 120 Δ Δ Δ Δ ∘ ∘ Δ Δ 130 x x ∘ xΔ Δ ∘ Δ 140 x x Δ x Δ Δ Δ Δ 150 x x Δ x Δ Δ Δ Δ 160 x x x x Δ Δ x x 170x x x x Δ Δ x x (In Table, ∘ is for excellent, Δ for good, and x forunsuitable for use)

As can be confirmed by these results, a reflective liquid crystaldisplay device could be realized with high display quality by setting θ3to not less than 20° and not more than 70° or not less than 110° and notmore than 150°.

EXAMPLE 5

As Example 5, a reflective liquid crystal display device will bedescribed that includes a liquid crystal layer of which the twist angleof the twisted nematic liquid crystal is set to 70° and two opticalretardation compensator plates have retardation of 135 nm and 270 nmrespectively.

In Example 5, a reflective liquid crystal display device structured asshown in aforementioned FIG. 1 was fabricated. The light reflective film7 on a substrate 5 was made of aluminum and served as a light reflectiveelectrode. In addition, the liquid crystal drive cell was a 70° twistedliquid crystal layer 1 that was adjusted to have a thickness of 4.5 μmafter the introduction of liquid crystal, the introduced liquid crystalmaterial used here having the same liquid crystal physical properties(dielectric anisotropy, elasticity, viscosity, temperature properties,and voltage retaining property) as the liquid crystal used in a typicalTFT transmissive liquid crystal display device only except Δn which wasadjusted to 0.0667. Here, the product of the thickness of the liquidcrystal layer 1 and the birefringence difference of the liquid crystalwas set to 300 nm.

In the present example, the polarizer plate 10, the optical retardationcompensator plate 8, and the optical retardation compensator plate 9were configured in two kinds as shown in FIGS. 12( a) and 12(b), and twokinds of samples were fabricated accordingly. Note in FIGS. 12( a) and12(b) that, similarly to aforementioned FIG. 8, 11 refers to thetransmission axis direction of the polarizer plate 10, 12 refers to theslow axis direction of the optical retardation compensator plate 9, 13refers to the slow axis direction of the optical retardation compensatorplate 8, 14 refers to the direction of the alignment of the liquidcrystal molecules that are in contact with the alignment layer 2 formedon a substrate 4, i.e., that are in a close proximity of the alignmentlayer 2, and 15 refers to the direction of the alignment of the liquidcrystal molecules that are in contact with the alignment layer 3 formedon a substrate 5, i.e., that are in a close proximity of the alignmentlayer 3, and also that the figure is viewed from the direction of theincident light on the liquid crystal display device.

Further, the positional relationship of one of the samples, as shown inFIG. 12( a), stipulates that the angle, θ1, formed by the transmissionaxis direction 11 of the polarizer plate 10 and the slow axis direction13 of the optical retardation compensator plate 8 was set to 75°, theangle, θ2, formed by the transmission axis direction 11 of the polarizerplate 10 and the slow axis direction 12 of the optical retardationcompensator plate 9 was set to 15°, and the angle, θ3, formed by thealignment direction 14 of the liquid crystal molecules on the substrate4 and the transmission axis direction 11 of the polarizer plate 10 wasset to 40°. This sample will be called Sample #5 a.

The positional relationship of the other sample, as shown in FIG. 12(b), stipulates that the angle, θ1, formed by the transmission axisdirection 11 of the polarizer plate 10 and the slow axis direction 13 ofthe optical retardation compensator plate 8 was set to 75°, the angle,θ2, formed by the transmission axis direction 11 of the polarizer plate10 and the slow axis direction 12 of the optical retardation compensatorplate 9 was set to 15°, and the angle, θ3, formed by the alignmentdirection 14 of the liquid crystal molecules on the substrate 4 and thetransmission axis direction 11 of the polarizer plate 10 was set to130°. This sample will be called Sample #5 b. As a result, Samples #5 aand #5 b differed from each other in θ3 and shared common θ1 and θ2.

Note that as to these Samples #5 a and #5 b, similarly to aforementionedExample 3, the optical retardation compensator plate 8 and the opticalretardation compensator plate 9 were both formed from an oriented filmmade of polyvinylalcohol; the optical retardation compensator plate 8introduced a phase difference controlled to 130 nm to 140 nm to thelight having a wavelength of 550 nm that travelled therethrough in anormal direction, and the optical retardation compensator plate 9introduced a phase difference controlled to 265 nm to 275 nm to the samekind of light. In addition, as the polarizer plate 10, a polarizer platewas used that included an AR layer made up of multi-layered dielectricfilms and showed a transmittance of 45% when measured in a single piece.

A graph is shown in FIG. 13 illustrating voltage dependencies ofreflectance of the reflective liquid crystal display devices (Sample #5a and #5 b) arranged in the aforementioned manner. In FIG. 13, the curve13-1 represents measurement results of Sample #5 a, and the curve 13-2those of Sample #5 b. Note that the reflectance was measured, as shownin FIG. 10, using the same optical measuring system as in aforementionedExample 3 and also that the reflectance at 100% was set in the samemanner as in aforementioned Example 3. As can be understood from themeasurements shown in FIG. 13, a high reflectance was obtained at adrive voltage as low as about 1.5V or even lower; a comparison of thetwo curves shows that a higher reflectance was obtained with Sample #5 arepresented by the curve 13-1.

In addition, Table 4 shows results of the examination of voltage versusreflectance property on the reflective liquid crystal display devices(Samples #5 a and #5 b) of Example 5 as detailed here and the reflectiveliquid crystal display device of aforementioned Example 3.

TABLE 4 Brightness in Bright State Contrast Ratio Example 3 90% 10Example 5 95% 8 (Sample #5a) Example 5 95% 15 (Sample #5b)

As understood from Table 4, in either case, a sufficient reflectance andcontrast ratio was achieved in a bright state; the reflective liquidcrystal display devices were satisfactory in visual observation too.

Note that in Table 4 the contrast ratio is defined as the quotientobtained by dividing the reflectance in the bright state by thereflectance in the dark state. Here, the voltage that produces thehighest reflectance for each example was used as the voltage applied inthe bright state, while the voltage applied in the dark state was set to3V.

EXAMPLE 6

As Example 6, a reflective liquid crystal display device will bedescribed that was fabricated following the same conditions as in thosein aforementioned Example 4. Optical properties were measured on thereflective liquid crystal display device with different combinations ofΔn(450)/Δn(550) and Δn(650)/Δn(550), i.e., (1, 1), (1.003, 0.993),(1.007, 0.987), (1.01, 0.98), (1.03, 0.96), (1.06, 0.95), and (1.1,0.93), and the results are shown in Table 5. Note that Δn(450)/Δn(550)and Δn(650)/Δn(550) represent the ratios of the refractive indexanisotropies, Δn(450) and Δn(650), of the optical retardationcompensator plate 8 and the optical retardation compensator plate 9 withrespect to light having a wavelength of 450 nm and with respect to lighthaving a wavelength of 650 nm respectively to the refractive indexanisotropy, Δn(550), of the optical retardation compensator plate 8 andthe optical retardation compensator plate 9 with respect to light havinga wavelength of 550 nm.

TABLE 5 Δn(450)/Δn(550) Δn(650)/Δn(550) Properties 1 1 ∘ 1.003 0.993 ∘1.007 0.987 ∘ 1.01 0.98 Δ 1.03 0.96 Δ 1.06 0.95 Δ 1.1 0.93 x (In Table,∘ is for excellent, Δ for good, and x for unsuitable for use)

These results confirm that a reflective liquid crystal display devicedisplay could be made with high display quality by such settings tosatisfy the relationships:1≦Δn(450)/Δn(550)≦1.06,and0.95≦Δn(650)/Δn(550)≦1,and with even higher display quality by such settings to satisfy therelationships:1≦Δn(450)/Δn(550)≦1.007,and0.987≦Δn(650)/Δn(550)≦1.

EXAMPLE 7

As Example 7, a reflective liquid crystal display device will bedescribed that was fabricated following the same conditions as in thosein aforementioned Example 4. Brightness, contrast, coloring weremeasured, and overall evaluation was made on the reflective liquidcrystal display by altering the angle, θ4, formed by a direction 16 onthe plane defined by the viewing direction and the normal to the displaysurface shown in FIG. 14 and the direction 14 of the liquid crystalmolecules in a close proximity of the second substrate, and the resultsare shown in FIG. 15. The results confirm that a reflective liquidcrystal display device was obtained with high display quality, inparticular, substantially excellent brightness, contrast, and parallaxfrom the achromatic axis by setting θ4 to not less than 0° and not morethan 30° or not less than 180° and not more than 210°.

EXAMPLE 8

As Example 8, the following description will explain an example using alight reflective film having smooth concavities and convexities and anactive matrix driving system.

FIG. 16 is a cross-sectional view showing a structure of a major part ofa reflective liquid crystal display device of Example 8. As shown inFIG. 16, the reflective liquid crystal display device 16 included afirst substrate 5 and a second substrate 4 that was made of transparentglass and further includes as an active switching element an TFT element17 formed on each pixel on the first substrate 5. On the TFT element 17and drive wires (not shown) were formed an interlayer insulating film18. The drain terminal (not shown) of the TFT element 17 waselectrically connected to a light reflective pixel electrode 19 via acontact hole. On the light reflective pixel electrode 19 was formed analignment layer 3 with a 100 nm thickness.

Here, the light reflective pixel electrode 19 was made of conductivemetal, such as aluminum, nickel, chromium, silver, and an alloyincluding one or more of these metals, and was light reflective.Further, as to the shape, the light reflective pixel electrode 19 hadsmooth concavities and convexities at a portion where there was providedno contact hole so as to prevent the metallic reflecting surface fromserving as a specular surface.

Next, a method of forming the light reflective pixel electrode 19 willbe explained in detail.

Relatively large protrusions 20 and relatively small protrusions 21 weremade in great numbers from photosensitive resin material on the surfaceof the substrate 5 on which the TFT elements 17 and the drive wires (notshown) had been fabricated in advance. The relatively large protrusions20 and relatively small protrusions 21 were formed in great numbers in acircular shape using photolithography technique so as to have bottomdiameters of D1 and D2 respectively (see FIG. 16). The D1 and D2 wereset to 5 μm and 3 μm respectively for example. In addition, theinterval, D3, between the protrusions was set to 2 μm or greater. Inaddition, the heights of the protrusions, which were controllable duringfabrication of the film from photosensitive resin material, was set to1.5 μm in the present example, and the heads of the protrusions weremade smooth in exposure and baking processes that followed.

Subsequently to this, the protrusions 20 and 21 were covered, and aplanarization layer 22 was formed from a similar photosensitive resinmaterial to plug the flat portion between the protrusions 20 and 21.Hence, the surface of the planarization layer 22, being affected by theprotrusions 20 and 21, had a smoothly curved surface, that was therequired target shape. Note that the protrusion and the planarizationlayer 22 were not fabricated in the contact hole portion.

Through the fabrication of the TFT element substrate 23 having such astructure, a reflective liquid crystal display device that had a highso-called aperture ratio and was therefore bright was obtained whereinno parallax existed because the light reflective pixel electrode 19doubled as a reflector plate and was disposed near the liquid crystallayer 1, and no light, having passed through the liquid crystal layer 1and reflected at the light reflective pixel electrode 19, was damaged bythe TFT element 17 and the element drive wires (not shown) portion.

In contrast, the other substrate, which was used in combination with theTFT element substrate 23, included a highly bright color filter 24 inaccordance with a reflective mode. The color filter 24 was provided witha black matrix 25 that prevented color mixture between the pixels andleakage of reflected light in a dark display caused by no-voltageapplied portions between pixel electrodes and electric fielddisturbance.

The black matrix 25, even if being made from an inexpensive metal filmfor example, did not reflect light to degrade visibility, since theincident light, which was already substantially circularly polarized,was reflected at the black matrix 25, and then absorbed again by thepolarizer plate upon exiting, due to the function of the opticalretardation compensator plate. Note that the black matrix 25, if beingfurther subjected to a low reflection process, was more preferable to beused for a high contrast display.

Opposite electrodes 6 were formed, on the color filter 24 in such amanner to oppositely face the light reflective pixel electrode 19, witha 140 nm thickness and a desired pattern to drive the TFT elements, bymask depositing ITO (Indium Tin Oxide) as a transparent electrode 6using a sputtering technique. Then an alignment layer 2 was formedfurther thereon, which completed the process to fabricate a color filtersubstrate 26.

Note that even if the transparent electrode 6 had a thickness other than140 nm, since part of incident light that was reflected without reachingthe liquid crystal layer 1 due to interference effects by the thicknessof the transparent electrode 6 was absorbed by the optical retardationcompensator plates 8 and 9 and the polarizer plate 10, there were noadverse effects on a dark state, and visibility did not deteriorate.

In addition, the color filter 24 used here was suitably designed toproduce brightness that was suited for high contrast display mode usinga polarizer plate, and the color filter substrate 26 had a transmittanceof 50% at Y value with the black matrix 25 having an aperture ratio of90%.

The TFT element substrate 23 and the color filter substrate 26 preparedin this manner were subjected to an alignment layer treatment throughrubbing, a process to dispose plastic spacers (not shown) formaintaining the thickness of the liquid crystal layer 1, and a processto dispose a sealing material along edges, and thereafter were alignedwith each other so as to oppositely face each other, and sealed throughcuring under pressure, so as to prepare a liquid crystal cell into whichliquid crystal would be filled. Further, in the liquid crystal layer 1,liquid crystal material having a positive dielectric anisotropy Δε wasintroduced using vacuum filling. Hereinafter, the direction around theliquid crystal display device would be described as viewed by a viewerwho oppositely faced the device, with the upward direction being definedas the 12 o'clock direction in reference to a clock face.

On a side of the color filter substrate 26, opposite to the liquidcrystal layer 1, were disposed optical retardation compensator plates 8and 9 that were formed from an oriented film made of polyvinylalcohol. Apolarizer plate 10 was disposed further on the optical retardationcompensator plates 8 and 9.

In the present example, the polarizer plate 10, the optical retardationcompensator plate 8, and the optical retardation compensator plate 9,which constituted the circular polarizer plate 100, were configured asshown in FIG. 17. Note in FIG. 17 that 11 refers to the transmissionaxis direction of the polarizer plate 10, 12 refers to the slow axisdirection of the optical retardation compensator plate 9, 13 refers tothe slow axis direction of the optical retardation compensator plate 8,14 refers to the direction of the alignment of the liquid crystalmolecules that are in contact with an alignment layer 2 formed on thecolor filter substrate 26, i.e., that are in a close proximity of thealignment layer 2, and 15 refers to the direction of the alignment ofthe liquid crystal molecules that are in contact with an alignment layer3 formed on the TFT element substrate 23, i.e., that are in a closeproximity of the alignment layer 3. Here, the alignment layer 2 on thecolor filter substrate 26 is fabricated so that the alignment processingdirection 14 is in the 3 o'clock direction relative to the device.

Further, the positional relationship, as shown in FIG. 17, stipulatesthat the angle, θ1, formed by the transmission axis direction 11 of thepolarizer plate 10 and the slow axis direction 13 of the opticalretardation compensator plate 8 was set to 75°, the angle, θ2, formed bythe transmission axis direction 11 of the polarizer plate 10 and theslow axis direction 12 of the optical retardation compensator plate 9was set to 15°, and the angle, θ3, formed by the alignment direction 14of the liquid crystal molecules on the color filter substrate 26 and thetransmission axis direction 11 of the polarizer plate 10 was set to130°.

In addition, the liquid crystal layer 1 used here was adjusted to have athickness of 4.0 to 5.0 μm after the introduction of liquid crystalmaterial, the liquid crystal used here had a Δn of 0.0667, the productof the thickness of the liquid crystal layer and the birefringencedifference was set to substantially 300 nm. The thickness of the liquidcrystal layer 1 differed depending on the place due to the concave andconvex surface of the light reflective pixel electrode 19.

Further, a drive circuit was mounted around the liquid crystal displayfabricated in the above manner to complete the process of fabricate areflective liquid crystal display device.

In the reflective liquid crystal display device of the present example,since the light reflective pixel electrode 19 was located near theliquid crystal layer 1, there was no parallax being produced, and asatisfactorily high resolution display was realized. Those concavitiesand convexities provided to the light reflective pixel electrode 19prevented the viewer from being reflected in the device, therebyrealizing a satisfactory white display. Further, since nothing wasdisposed in front of the liquid crystal display device to randomlyreflect incident light, the liquid crystal display device showed asatisfactory dark state. For these reasons, the liquid crystal displaydevice achieved a high contrast ratio display.

In addition, since a highly bright color filter 24 was used, even when apolarizer plate was used, sufficient brightness could be ensured, thereflectance was low in the dark state, and color purity did notdeteriorate because of the simultaneous viewing of the light reflectedon color elements selected to this dark state and the light reflected onthe color elements selected to a bright state. This allowed a highlysatisfactory color reproduction without damaging the color reproductionrange of the color filter 24 despite the poor saturation of the highlybright color filter 24.

In addition, since the voltage applied across the pixels were set to anintermediate state between a dark state and a bright state, there wereno problems in producing gray scales. Therefore, there were no problemsin reproducing half tones with the colors of the color filter 24. Inaddition, it was confirmed that in actual driving the response speedposed no problems in reproducing moving pictures.

As mentioned above, a reflective liquid crystal display device could beobtained, using a practicable fabrication method, that could displayhalf-tones and moving pictures while maintaining a satisfactory colorreproduction range.

EXAMPLE 9

As Example 9, a reflective liquid crystal display device will bedescribed that is an example to enhance brightness through thefabrication of a concave and convex light reflective film having anin-plane anisotropy and to specify the direction in which the inclinedviewing angle of the liquid crystal layer is satisfactory to a directionin which the brightness is high.

In Example 9, the light reflective pixel electrode 19 of the reflectiveliquid crystal display device was fabricated to have concavities andconvexities according to a pattern different from that in Example 8, sothat the concavities and convexities varied depending on the directionon the plane on which the reflective electrodes were formed.

In the present example, a pattern was formed that satisfied theaforementioned conditions, as shown in the major-part-showing enlargedplan view constituting FIG. 18, wherein the convexities were notcircular, but elliptical, and had properties that are dependent todirections. Reflection property was measured on a light reflector plateconstituted only by a light reflective film having such concavities andconvexities, using a measuring system shown in FIG. 19. To be morespecific, as shown in FIG. 19, illumination light was directed to enterfrom a 30° oblique direction, and the intensity of reflected light wasmeasured in the normal direction to the light reflector plate surface byrotating the light source to detect reflective anisotropy.

The results, shown in FIG. 20, confirm that the light from a particulardirection was efficiently guided toward the front of the liquid crystaldisplay device. It should be noted, however, that considering that therefractive index of the liquid crystal material was greatly differentfrom that of air, immersion oil (matching oil) having a refractive indexof 1.516 was dropped on the light reflector plate surface and atransparent glass was attached thereonto for measurement. In addition,measured values were subjected to a conversion so that 100% wouldrepresent the value obtained when measurement was made in the samemanner on a perfect reflecting diffuser (standard white board) made ofMgO. In FIG. 20, the curve 20-1 represents measured and then convertedvalues for the anisotropic diffuse reflector plate of the presentexample, and the curve 20-2 represents measured and then convertedvalues for a diffuse reflector plate similar to that used in Example 8.

The results are shown in FIG. 20. With the curve 20-1 representing sucha reflector plate of the present example that the concavities andconvexities are formed at a mean cycle that varies according to thedirection on the reflector plate surface, the reflective brightness(reflected light intensity) changes greatly with a change in theincident direction, φ, of illumination light. In contrast, with thecurve 20-2 representing such a reflector plate (Example 8) that theconcavities and convexities are formed isotropically, the reflectivebrightness (reflected light intensity) does not change greatly with achange in the incident direction, φ, of illumination light.

From these results, the inventors of the present invention have foundthat the direction dependent property (anisotropy), where the meanconcavity and convexity cycle varies according to the direction on thereflector plate surface as can be seen with the reflector plate used inthe present example, is useful means to increase reflective brightness.Further, in FIG. 20 the directions φ=90° and 270° in which the meancycle of the concavities and convexities is short; it has been thusconfirmed that illumination light from a direction in which the meancycle is short has high reflective brightness.

Four kinds of samples were fabricated by forming alignment films 2 and 3in the same manner as in Example 8 on a TFT element substrate 23 havinga light reflector plate characterized by these features and on a colorfilter substrate 26 fabricated in the same manner as in Example 8, andthen subjecting the substrates 23 and 26 to an alignment layer treatment(the twist angle 70°).

The samples differed from each other in the configuration of thepolarizer plate 10, the optical retardation compensator plate 8, and theoptical retardation compensator plate 9, as shown in FIGS. 21( a) to21(d). Note in FIGS. 21( a) to 21(d) that, similarly to aforementionedFIG. 17, 11 refers to the transmission axis direction of the polarizerplate 10, 12 refers to the slow axis direction of the opticalretardation compensator plate 9, 13 refers to the slow axis direction ofthe optical retardation compensator plate 8, 14 refers to the directionof the alignment of the liquid crystal molecules that are in contactwith an alignment layer 2 formed on the color filter substrate 26, i.e.,that are in a close proximity of the alignment layer 2, and 15 refers tothe direction of the alignment of the liquid crystal molecules that arein contact with an alignment layer 3 formed on the TFT element substrate23, i.e., that are in a close proximity of the alignment layer 3. Thesefigures are viewed from the direction in which light enters the liquidcrystal display device.

In other words, as to a sample shown in FIG. 21( a), the positionalrelationship stipulates that the angle, θ1, formed by the transmissionaxis direction 11 of the polarizer plate 10 and the slow axis direction13 of the optical retardation compensator plate 8 was set to 75°, theangle, θ2, formed by the transmission axis direction 11 of the polarizerplate 10 and the slow axis direction 12 of the optical retardationcompensator plate 9 was set to 15°, and the angle, θ3, formed by thealignment direction 14 of the liquid crystal molecules on the colorfilter substrate 26 and the transmission axis direction 11 of thepolarizer plate 10 was set to 130°. This sample will be referred to asSample #9 a (the same as Example 8). Note that the alignment direction14 of the liquid crystal molecules on the color filter substrate 26 wasset parallel to the 3 o'clock direction.

Further, as to a sample shown in FIG. 21( b), the positionalrelationship stipulates that the angle, θ1, formed by the transmissionaxis direction 11 of the polarizer plate 10 and the slow axis direction13 of the optical retardation compensator plate 8 was set to 75°, theangle, θ2, formed by the transmission axis direction 11 of the polarizerplate 10 and the slow axis direction 12 of the optical retardationcompensator plate 9 was set to 15°, and the angle, θ3, formed by thealignment direction 14 of the liquid crystal molecules on the colorfilter substrate 26 and the transmission axis direction 11 of thepolarizer plate 10 was set to 130°. This sample will be referred to asSample #9 b. Note that the alignment direction 14 of the liquid crystalmolecules on the color filter substrate 26 was set parallel to the 12o'clock direction.

Further, as to a sample shown in FIG. 21( c), the positionalrelationship stipulates that the angle, θ1, formed by the transmissionaxis direction 11 of the polarizer plate 10 and the slow axis direction13 of the optical retardation compensator plate 8 was set to 75°, theangle, θ2, formed by the transmission axis direction 11 of the polarizerplate 10 and the slow axis direction 12 of the optical retardationcompensator plate 9 was set to 15°, and the angle, θ3, formed by thealignment direction 14 of the liquid crystal molecules on the colorfilter substrate 26 and the transmission axis direction 11 of thepolarizer plate 10 was set to 40°. This sample will be referred to asSample #9 c. Note that the alignment direction 14 of the liquid crystalmolecules on the color filter substrate 26 was set parallel to the 3o'clock direction.

Further, as to a sample shown in FIG. 21( d), the positionalrelationship stipulates that the angle, θ1, formed by the transmissionaxis direction 11 of the polarizer plate 10 and the slow axis direction13 of the optical retardation compensator plate 8 was set to 75°, theangle, θ2, formed by the transmission axis direction 11 of the polarizerplate 10 and the slow axis direction 12 of the optical retardationcompensator plate 9 was set to 15°, and the angle, θ3, formed by thealignment direction 14 of the liquid crystal molecules on the colorfilter substrate 26 and the transmission axis direction 11 of thepolarizer plate 10 was set to 40°. This sample will be referred to asSample #9 d. Note that the alignment direction 14 of the liquid crystalmolecules on the color filter substrate 26 was set parallel to the 12o'clock direction.

Note that the samples were fabricated in the same manner as inaforementioned Example 8, except the process in which concave and convexpatterns were fabricated on the light reflector plates.

Visual observation of these sample reflective liquid crystal displaydevices that included the light reflector plates having such concavitiesand convexities revealed that a display was realized with a higherbrightness with Samples #9 a to #9 d than with foregoing Example 8 whenviewed from the front direction, and also revealed that anisotropicconcavities and convexities enhanced brightness. In such an event,reflective brightness was high when illumination light entered in the 12o'clock direction or the 6 o'clock direction. Further, brightness wassimilarly high when the devices were illuminated from the frontdirection and viewed from the oblique 12 or 6 o'clock direction.

Further, the sample liquid crystal display devices were illuminated fromthe front direction with incident illumination light and viewed fromvarious oblique angles that were 45° off the front direction; Samples #9a and #9 d achieved a satisfactory display in the 6 and 12 o'clockdirections that were oblique directions in which reflective brightnesswas high, and also achieved a satisfactory contrast in display in thesame directions, whereas when viewed from an oblique viewing directionin which brightness was high, the samples did not seemingly show anyparticular inclination-induced changes in the display. In contrast,observation revealed that Samples #9 b and #9 c degraded the contrastratios in display when viewed from the 6 or 12 o'clock direction inwhich brightness was high.

This shows that the viewing angle direction in which the liquid crystaldisplay modulation layer (the liquid crystal layer 1) showed excellentvisibility varied according to the three different values of θ3. Inaddition, Samples #9 a and #9 d, wherein the direction to givesatisfactory visibility coincided with the direction in which theanisotropic concavities and convexities of the light reflector plateyielded high brightness, realized a high quality display featuring thehigh contrast ratio of the polarizer plate, the optical retardationcompensator plate, and the liquid crystal modulation layer (the liquidcrystal layer) in accordance with the present invention.

Note that the direction of the anisotropic concavities and convexitiesof the light reflector plate employed in the present example may be setdifferently according to principal ambient conditions in which theliquid crystal display device in accordance with the present inventionis actually used; in such a case, needless to say, in order to obtainthe same effects, the angles formed by the alignment of the liquidcrystal, the polarizer plate, and the optical retardation compensatorplate should be set so that the direction giving satisfactory obliqueviewing angle properties coincides with the direction yielding highbrightness.

EXAMPLE 10

Next, as Example 10, the following description will explain an exampleof a reflective liquid crystal display device incorporating a touchpanel as information input means installed in a personal digital tool,which is a major application field of the reflective liquid crystaldisplay device in accordance with the present invention.

First, a reference is made to FIG. 22 constituted by a cross-sectionalview schematically showing a major part of an arrangement of a touchpanel used in the present example. As shown in FIG. 22, the touch panel31 was a planar pressure sensitive element including a supportingsubstrate 28 on which a transparent electrode 30 was formed fordetecting a pressed position and a movable substrate 27 on which atransparent electrode 29 was formed for detecting a pressed position,the transparent electrodes 29 and 30 being disposed so as to oppositelyface each other with an air gap sandwiched therebetween. Note that boththe movable substrate 27 and the supporting substrate 28 used here hadno birefringence.

A major part of the structure of the present example is schematicallyshown in a cross-sectional view constituting FIG. 23. As shown in FIG.23, a reflective liquid crystal display device incorporating a touchpanel of the present example included an optical retardation compensatorplate 8, an optical retardation compensator plate 9, and a polarizerplate 10 being attached onto the movable substrate 27 of the touch panel31, and all these were disposed on the display surface side of a liquidcrystal drive cell having the same structure as the liquid crystaldisplay device of aforementioned Example 8 except that no polarizerplate and no optical retardation compensator plates 8 and 9 wereattached.

In such an event, the alignment direction of the liquid crystal layer 1,the polarizer plate 10, and the optical retardation compensator plates 8and 9 were configured in the same manner as in aforementioned FIG. 17(Example 8), and further, the same arrangement was done except the touchpanel. Note that an air gap 32 was provided so as to maintain thedistance between the supporting substrate 28 of the touch panel and thecolor filter substrate 26 of the reflective liquid crystal displaydevice and to thereby produce a pressure propagation prevention effect,the pressure on the touch panel being prevented from propagating to acolor filter substrate 26, without using a pressure buffering memberwhich otherwise would have added to the weight of the device.

In addition, as a comparative example, a reflective liquid crystaldisplay device incorporating a touch panel was fabricated including astructure whose major part is shown in a cross-sectional viewconstituting FIG. 24. In other words, the structure of the comparativeexample was equivalent to the touch panel 31 shown in FIG. 22 beingdisposed on the polarizer plate 10 of the liquid crystal display devicehaving the structure of aforementioned Example 8. Therefore, the onlydifference between the present example and the comparative example wasthe relative position of the touch panel 31.

Next, comparison was made between the present example and thecomparative example. First, as to the comparative example, the lightcomponent reflected at the touch panel was directly viewed, therebygreatly degrading visibility. That reflected light included the lightreflected due to the gap sandwiched between the touch panel supportingsubstrate 28 and the polarizer plate 10 as well as the light reflecteddue to the gap sandwiched between the transparent electrodes 29 and 30.

In contrast, as to the present example, no reflected light component,such as that occurred with the comparative example, was observed; a verysatisfactory display was observed similarly to the case where no touchpanel is used (Example 8). Further as to the present example, unlike thecomparative example, no light was observed to be reflected due to thegap sandwiched between the transparent electrodes 29 and 30.

Further, no reflection was observed either at the interface between theair gap 32 for preventing pressure propagation and the touch panelsupporting substrate 28 nor at the interface between the touch panelsupporting substrate 28 and the color filter substrate 26 of the liquidcrystal display device. Therefore, according to Example 10, a reflectiveliquid crystal display device incorporating an input device (touchpanel) was realized that was lightweight because of the lack of need fora pressure buffering member, and effectively utilized, for display, acircularly polarized state of light created by reflection preventivemeans of the input device.

In addition, a more convenient and lightweight arrangement was feasible,if, to mention briefly, the movable substrate 27 of the touch panel 31was omitted, and the transparent electrode 29 was directly disposed onthe liquid crystal layer side of the optical retardation compensatorplate 8.

Second Embodiment of the Invention

Referring to drawings, the following description will explain anotherembodiment in accordance with the present invention. For convenience,members of the present embodiment that have the same function as membersof the previous embodiment are indicated by the same reference numeralsand description thereof is omitted.

So far, the description has discussed examples wherein as to the casewhen substantially high voltage is applied across the liquid crystallayer, the liquid crystal layer has no polarized light conversionfunction, and satisfactory property is obtained in such approximation.However, considering that the voltage applied across the liquid crystalhas practical limitations, optimization in detail is more effective.

To be more specific, referring to aforementioned FIG. 1, a black displayis achieved when the voltage applied across the liquid crystal is at itsmaximum value; the liquid crystal here does not entirely align in thesubstrate normal direction, and a consideration should be given to thecomponent parallel to the substrates 4 and 5 remaining in the alignmentof the liquid crystal. Conditions for a dark display with this takeninto consideration are, similarly to cases above, that in a state wherea practically maximum voltage is applied across the liquid crystal, theincident light entering the polarizer plate 10 be circularly polarizedafter passing both the optical retardation compensator plates 8 and 9and the liquid crystal layer 1.

In this state, since a practically maximum voltage is applied across theliquid crystal 1, the liquid crystal display device is in a state whereno polarized light conversion function is produced. However, thereremains a little polarized light conversion function (hereinafter, willbe referred to as a residual phase difference) in accordance with thecomponent of the alignment of the liquid crystal that is parallel to thesubstrate. By slightly modifying the previous conditions for the opticalretardation compensator plates 8 and 9 to conform to this, asatisfactory dark display is achieved at practically maximum voltage.

In contrast, conditions to realize a satisfactory bright display usingthe optical retardation compensator plates 8 and 9 and the alignment ofthe liquid crystal layer 1 that are optimized so as to achieve asatisfactory dark display in the above manner are similarly that thepolarization state on the surface of the reflector plate 3 be linearlypolarized. However, design parameters for the liquid crystal layer 1 tosatisfy those conditions are still decided on the same assumption thatsuch a sufficiently high voltage can be applied that the residualbirefringence of the liquid crystal becomes ignorable.

In other words, in a case where the optical retardation compensatorplates 8 and 9 are used that are slightly modified in accordance withthe residual phase difference of the liquid crystal, the specificationsfor the liquid crystal layer 1 do not greatly differ from those beforethe modification, and are predicable from the previous specifications.

FIG. 25 shows schematically an arrangement of a reflective liquidcrystal display device of the present example. As shown in FIG. 25, thereflective liquid crystal display device, including the arrangement ofthe reflective liquid crystal display device of aforementionedEmbodiment 1, is arranged to have a third optical retardationcompensator plate 101 between the substrate 4 and the opticalretardation compensator plate 8 of the circular polarizer plate 100 tocancel the residual phase difference of the liquid crystal layer 1. FIG.26 shows a configuration example of the three optical retardationcompensator plates 8, 9, and 101 in the reflective liquid crystaldisplay device.

As to the direction of the slow axis of the residual phase difference ofthe liquid crystal layer 1, if the twist angle of the liquid crystallayer 1 is set to about 70°, which is approximately the middle value ofthe setting range for the twist angle in accordance with the presentinvention, there remains a birefringence component of the slow axiswhich is parallel to the alignment direction of the liquid crystalbetween the centers of the substrates 4 and 5 of the liquid crystallayer 1. To cancel this, an optical retardation compensator plate havinga slow axis in a direction perpendicular to the alignment of the liquidcrystal is appropriately disposed as the third optical retardationcompensator plate 101. Although depending on the maximum voltage appliedacross the liquid crystal, the residual phase difference of the liquidcrystal layer 1 can be cancelled if the magnitude of retardation is setto approximately 10 to 50 nm.

Next, the following description further discusses a method of achievinga satisfactory display by improving the viewing angle characteristicwith the reflective liquid crystal display device shown in FIG. 25.

In the reflective liquid crystal display device shown in FIG. 25, asatisfactory dark display is achieved at a maximum value of an actualdriving voltage; according to a method whereby a satisfactory display isobtained in this manner, in a state where a sufficient voltage isapplied across the liquid crystal layer 1, the cancellation of theresidual birefringence of the liquid crystal is effective.

Therefore, the viewing angle becomes expandable by expanding such aviewing angle range that the residual birefringence of the liquidcrystal layer 1 can be satisfactorily cancel. In order to achieve this,the use of an optical retardation compensator plate is effective withthe three-dimensional configuration of the alignment of liquid crystalbeing taken into consideration.

FIG. 27 shows schematically a three-dimensional alignment in an actualdriven state of the liquid crystal layer 1. Note that FIG. 27 shows thealignment of the liquid crystal of the reflective liquid crystal displaydevice shown in FIG. 25 more faithfully to the actual alignment. In sucha state, the residual birefringence of the light passing through theliquid crystal layer 1 in the normal direction of the display surfacecan be cancel by a uniaxial optical retardation compensator plate havingthe slow axis direction thereof on an ordinary plane; however, as to thelight obliquely passing through the liquid crystal layer 1, the use ofan optical retardation compensator plate is effective with theinclination of the alignment of the liquid crystal layer 1 being furthertaken into consideration.

First, since the liquid crystal aligns approximately perpendicular tothe substrates 4 and 5, the refractive index of the liquid crystal layer1 has a large component with respect to the electric field that is inthe substrate normal direction. In order to cancel this, an opticalretardation compensator plate having a smaller refractive index withrespect to the electric field that is in the layer thickness directionof the third optical retardation compensator plate 101 is effective;this is achieved by employing an optical retardation compensator platethat is optically uniaxial and has a smaller refractive index withrespect to the electric field that is in a film thickness direction thanwith respect to the electric field that is in a film surface directionas the optical retardation compensator plate 101. Further, the opticalretardation compensator plate 101 may be an optically biaxial indexellipsoid with the purpose of canceling the residual phase difference ofthe aforementioned liquid crystal layer in a direction on a layersurface.

In addition, more strictly, it is effective to take into account thatthe alignment of the liquid crystal is not completely perpendicular tothe substrates 4 and 5. Especially when a diffuse reflector film or areflective film are configured obliquely to the display surface of thereflective liquid crystal display device, or more generally when such areflecting surface is used that has a function to reflect light in adirection other than the specular reflection direction of the displaysurface, it is effective in achieving a satisfactory viewing anglecharacteristic to cancel the residual birefringence of the liquidcrystal with respect to the optical path that extends from thetransmission through the liquid crystal layer 1 to the arrival to thelight reflective film 7 and also with respect to the outgoing opticalpath that extends from the light reflective film 7 to the transmissionthrough the liquid crystal layer 1.

Referring to FIG. 28, a more detailed explanation will be given. Asillustrated in FIG. 28, changes in illumination-associated environmentbrought onto the viewer who is in the front direction of the reflectiveliquid crystal display device as a result of the switching ofillumination from ambient illumination light A to illumination lightwhich is principally composed of illumination light B will be examined.

In such an event, while the viewer and the liquid crystal display deviceare fixed in position, the brightness and hue in a dark display alterwith a change in the ambient illumination light. This is because theresidual birefringence of the liquid crystal is cancel to a variabledegree according to the direction of the optical path in the liquidcrystal layer 1 through which light passes; a more satisfactory displaycan be achieved by preventing this from happening.

EXAMPLE 11

As Example 11, two Samples #11 a and #11 b were obtained by fabricatingreflective liquid crystal display devices incorporating the arrangementshown in aforementioned FIG. 25 in accordance with the parameters listedin Table 6.

TABLE 6 Sample Parameter #11a #11b Δnd (nm) 260 260 θ3 (°) 40 40 TwistAngle (°) 70 60 Angle, θ1, of Optical Retardation 75 75 CompensatorPlate 8 (°) Retardation Caused by Optical 135 nm 135 nm RetardationCompensator Plate 8 Angle, θ2, of Optical Retardation 15 15 CompensatorPlate 9 (°) Retardation Caused by Optical 270 nm 270 nm RetardationCompensator Plate 9 θ5 (°) 165 165 Retardation Caused by Optical 30 nm30 nm Retardation Compensator Plate 101

FIG. 29 shows voltage versus reflectance curves for Samples #11 a and#11 b. For comparison, FIG. 29 also shows a voltage versus reflectancecurve for the reflective liquid crystal display device of Example 3.

It is understood from this that as to Sample #11 a of the presentexample, the reflectance slightly decreased in a bright display, but asatisfactory dark display was achieved and also that as to Sample #11 b,the brightness did not decrease and a satisfactory dark display wasachieved.

Here, a further research was made to replace the two optical retardationcompensator plates 101 and 8 with only one optical retardationcompensator plate that offered the same function as the two plates,which would eventually enable the fabrication of liquid crystal displaydevices having the same function as these arrangement examples at lowercosts through reducing the number of optical retardation compensatorplates used.

In such an event, the inventors exploited the fact that two opticalretardation compensator plates can be substituted for a single opticalretardation compensator plate that has a retardation equivalent to thesum of the retardations of the two optical retardation compensatorplates if the two optical retardation compensator plates are stacked sothat their slow axes are parallel to each other, and can be substitutedfor a single optical retardation compensator plate that has aretardation equal to the difference between the retardations of the twooptical retardation compensator plates if the optical retardationcompensator plates are stacked so that their slow axes are perpendicularto each other.

In other words, since the optical retardation compensator plate 8 andthe optical retardation compensator plate 101 in Sample #11 b of thepresent example were configured so as to be stacked in a close proximityand also so that the slow axis directions were perpendicular to eachother, a single optical retardation compensator plate having aretardation equal to the retardation of the two plates could replace thetwo plates. In other words, by changing the retardation of the opticalretardation compensator plate 8, the same effects resulted as Samples#11 a and #11b, etc.

To confirm these effects, Samples #11 c and #11 d were additionallyfabricated. Samples #11 c and #11 d each had the cross-sectionalstructure as that shown in FIG. 1 mentioned in aforementionedEmbodiment 1. Table 7 shows the configuration of the optical retardationcompensator plates 8 and 9 in Samples #11 c and #11 d.

TABLE 7 Sample Parameter #11c #11d Δnd (nm) 260 260 θ3 (°) 45 135 TwistAngle (°) 60 60 θ3 (°) 75 75 Retardation Caused by Optical 105 165Retardation Compensator Plate 8 θ2 15 15 Retardation Caused by Optical270 nm 270 nm Retardation Compensator Plate 9

The voltage versus reflectance curves of Samples #11 c and #11 d aresimilar to that of Sample #11 b shown in FIG. 29.

This shows that a more satisfactory property can achieved byadditionally including a third optical retardation compensator plate andthereby cancelling the residual phase difference of liquid crystalacross which a practically maximum voltage is being applied. Further, itis confirmed that when two optical retardation compensator plates are inuse, similar effects can be achieved by adjusting retardation. In otherwords, it is confirmed that a more satisfactory black display can beachieved by the addition and adjustment of an optical retardationcompensator plate with actual driving being taken into account.

EXAMPLE 12

In Example 12, an optically uniaxial optical retardation compensatorplate having an inclined optical axis was used as the third opticalretardation compensator plate 101 so as to cancel the residualbirefringence of the liquid crystal layer 1 in more directions. Theresultant reflective liquid crystal display device including thearrangement shown in FIG. 30 was designated as Sample #12 a. Inaddition, a biaxial optical retardation compensator plate was used asthe third optical retardation compensator plate 101 to obtain areflective liquid crystal display device having the arrangement shown inFIG. 31, which was designated as Sample #12b.

In this example, the index ellipsoid of the optical retardationcompensator plate 101 was not inclined to the substrate.

Here, a concave and convex reflector plate made of metal (not shown) wasused as the light reflective film 7 similarly to the reflective liquidcrystal display device shown in FIG. 16 so as to provide a lightdiffusion property.

In addition, as Sample #12 c, a reflective liquid crystal display devicewere fabricated having the same arrangement as Samples #12 a and #12 b,except that a positively uniaxial optical retardation compensator platewas used as the optical retardation compensator plate 101.

Table 8 shows the configurations of optical elements of Samples #12 a to#12 c.

TABLE 8 Sample Parameter #12a #12b #12c Δnd (nm) 260 260 260 θ3 (°) 4545 45 Twist Angle (°) 60 60 60 θ1 (°) 75 75 75 Retardation Caused by 135nm 135 nm 135 nm Optical Retardation Compensator Plate 8 Angle, θ2, ofOptical 15 15 15 Retardation Compensator Plate 9 (°) Retardation Causedby 270 nm 270 nm 270 nm Optical Retardation Compensator Plate 9 Type ofOptical Retardation Inclined, Biaxial Negative, Compensator Plate 101negative, uniaxial uniaxial Angle, θ5, of Optical 165* 165* 165*Retardation Compensator Plate 101 (°) Retardation Caused by 30 nm* 30nm* 30 nm* Optical Retardation Compensator Plate 101 *The directions ofthe optical retardation compensator plates 101 of Samples #12a and #12brepresent attachment directions in the x-direction of the opticalretardation compensator plate, while the retardation of the opticalretardation compensator 101 represents the value with respect to lightpropagating in the substrate normal direction with the x-direction beingas the slow axis direction.

In addition, Table 9 shows results of the evaluation on Samples #12 a to#12 c regarding viewing angles characteristics.

TABLE 9 Sample Parameter #12a #12b #12c Bright Display White DisplayWhite Display White Display Viewed from Front Dark Display Viewed NoColoring Coloring Coloring from Front Caused by Observed Observed Changein Depending on Depending on Illumination Illumination IlluminationDirection. No Direction. No Direction. Increase in Increase in Increasein Reflectance Reflectance Reflectance in Black in Black in BlackDisplay Display Display Bright Display White Display White Display WhiteDisplay Viewed from Oblique Angle Dark Display Viewed Black DisplayBlack Display Black Display from Oblique Angle with no with Coloringwith Coloring Coloring for depending on depending on Every InclinationInclination Direction Direction Direction, Increasingly Bright withGreater Inclination

The optical retardation compensator plate 101 used in Sample #12 a wasfabricated through working on stretching process so that the indexellipsoid was inclined, and that the resultant light passing in thefront direction showed retardation of approximately 30 nm.

As shown in FIG. 30, the film showed a negative uniaxiality that onlythe refractive index for the z-component of the electric field wassmaller than the refractive indices for the other, i.e., x- and y-,components, and the z-direction was inclined from the normal directionof the optical retardation compensator plate 101 of a planar film. Theoptical retardation compensator plate 101 was configured so that thez-direction was similar to the direction of the alignment of the liquidcrystal at a practically maximum voltage, and the x-direction functionedas the slow axis to the light travelling in the front direction of theoptical retardation compensator plate 101.

The optical retardation compensator plate 101 satisfied(n _(y) −n _(z))d ₁₀₁=(n _(x) −n _(z))d ₁₀₁=300 nm,

-   -   where d₁₀₁ represents the thickness of the optical function        layer, and n_(x), n_(y), n_(z) represent the respective        refractive indices in the x-, y-, and z-directions shown in FIG.        30.

Further, needless to say, polymer film for fixing nematic liquidcrystalline alignment or discotic liquid crystalline alignment may beused to precisely cancel the three-dimensional alignment of the liquidcrystal layer 1.

The optical retardation compensator plate 101 used in Sample #12 b wasfabricated through working on stretching process so that the indexellipsoid was biaxial, and the resultant retardation with respect to theoptical axis for transmission in the front direction was approximately30 nm.

As shown in FIG. 31, the refractive indices of the film, with respect tothe components of an electric field, were the x-component, they-component, and the z-component in descending order of magnitude. Inaddition, (n_(x)−n_(y))d₁₀₁=30 nm, and (n_(y)−n_(z))d₁₀₁=300 nm.

As shown in Table 9, each bright display was a white display; however,the most satisfactory dark display was achieved with Sample #12 a,followed by Sample #12 b, then by Sample #12 c. In addition, an overallevaluation ranked Samples #12 a, #12 b, and #12 c in this order from themost satisfactory to less satisfactory. This is because in a whitedisplay the properties varied, but created no visual changes. Incontrast, in a black display, large visual changes were created,affecting the overall evaluation.

As mentioned above, it has been confirmed that a liquid crystal displaydevice can be achieved with a satisfactory viewing angle characteristicthrough working on the optical retardation compensator plate with thethree-dimensional alignment of the liquid crystal taken intoconsideration. It has been also confirmed that a more satisfactory darkstate can be achieved by rendering the optical retardation compensatorplates 8 and 9 biaxial.

Note, needless to say, in the present example that a retardationcompensator film may be used that double-functions as the opticalretardation compensator plate 8 and the optical retardation compensatorplate 101 to reduce costs similarly to Example 11.

INDUSTRIAL APPLICABILITY

As detailed so far, with the reflective liquid crystal display device inaccordance with the present invention, the reflecting surface of a lightreflector plate, such as a light reflective film, can be disposed on theliquid crystal layer side, and a satisfactory dark state can beobtained. Consequently, reflective liquid crystal display devices areobtainable that are free from parallax and displays high contrast, highresolution images, as well as moving pictures.

In addition, by adopting a color filter geared for high brightness inthe reflective liquid crystal display device in accordance with thepresent invention, a high quality, reflective-type color liquid crystaldisplay device is obtainable with a satisfactory color reproductioncapability.

In addition, with the reflective liquid crystal display deviceincorporating a touch panel in accordance with the present invention,when a touch panel is attached to the reflective liquid crystal displaydevice in accordance with the present invention, by employing a touchpanel constituted by a polarizer plate and two optical retardationcompensator plates, a high quality, reflective liquid crystal displaydevice incorporating a touch panel is obtainable with a capability toprevent reflected light from adversely affecting display properties.

As detailed so far, with the reflective liquid crystal display device inaccordance with the present invention, the reflecting surface of a lightreflector plate, such as a light reflective film, can be disposed on theliquid crystal layer side, and a satisfactory dark state can beobtained. Consequently, reflective liquid crystal display devices areobtainable that is free from parallax and displays high contrast, highresolution images, as well as moving pictures.

1. A liquid crystal display device, comprising: a liquid crystal layersandwiched between a first substrate having a light reflectibility and asecond substrate having a light transmissibility, the liquid crystallayer including twist-aligned nematic liquid crystal having a dielectricanisotropy; and a circularly polarizing unit, including a single linearpolarizer plate that selectively passes either right handed or lefthanded circularly polarized light out of natural light, wherein, thefirst substrate, the liquid crystal layer, and the circularly polarizingunit are stacked in this order to form at least a part of the liquidcrystal display device, the circularly polarizing unit is disposed suchthat a major surface of the circularly polarizing unit is on a liquidcrystal layer side, the circularly polarized light exiting thecircularly polarizing unit through the major surface when natural lightenters the circularly polarizing unit, a liquid crystal in the liquidcrystal layer has a birefringence difference, which, if multiplied by athickness of the liquid crystal layer, produces a product of not lessthan 85 nm and not more than 315 nm, and the liquid crystal layer has atwist angle in a range of 0° to 100°, wherein said incoming circularlypolarized light being linearly polarized at a surface of said firstsubstrate in a plurality of directions respectively representative ofsaid plurality of wave lengths of said natural light to thereby create adisplay.
 2. The liquid crystal display device as set forth in claim 1,wherein the circularly polarizing unit includes, a first opticalretardation compensator plate having a retardation in a substrate normaldirection set to not less than 100 nm and not more than 180 nm, and asecond optical retardation compensator plate having a retardation in asubstrate normal direction set to not less than 200 nm and not more than360 nm, the first optical retardation compensator plate, the secondoptical retardation compensator plate, and the linear polarizer platebeing stacked in this order when viewed from the liquid crystal layer,and |2×θ2−θ1| has a value not less than 35° and not more than 55° whereθ1 represents angle formed by a slow axis of the first opticalretardation compensator plate and either a transmission axis or anabsorption axis of the linear polarizer plate, and θ2 represents anangle formed by a slow axis of the second optical retardationcompensator plate and either the transmission axis or the absorptionaxis of the linear polarizer plate.
 3. The liquid crystal display deviceas set forth in claim 2, wherein the twist angle of the liquid crystallayer is in a range of 60° to 100°, the product of the birefringencedifference of the liquid crystal in the liquid crystal layer and thethickness of the liquid crystal layer is not less than 250 nm and notmore than 330 nm, and either the transmission axis or the absorptionaxis of the linear polarizer plate forms an angle, θ3, of not less than20° and not more than 70°, or not less than 110° and not more than 150°with an alignment direction of the liquid crystal molecules in a closeproximity of the second substrate.
 4. A liquid crystal display device,comprising: a liquid crystal layer sandwiched between a first substratehaving a light reflectibility and a second substrate having a lighttransmissibility, the liquid crystal layer being composed oftwist-aligned nematic liquid crystal having a dielectric anisotropy; anda circularly polarizing unit, including a single linear polarizer plate,that selectively passes either right handed or left handed circularlypolarized light out of natural light, wherein, the first substrate, theliquid crystal layer, and the circularly polarizing unit are stacked inthis order to form at least a part of the liquid crystal display device,the circularly polarizing unit is disposed such that a major surface ofthe circularly polarizing unit is on a liquid crystal layer side, thecircularly polarized light exiting the circularly polarizing unitthrough the major surface when natural light enters the circularlypolarizing unit, a liquid crystal in the liquid crystal layer has abirefringence difference, which, if multiplied by a thickness of theliquid crystal layer, produces a product of not less than 90 nm and notmore than 350 nm, and the liquid crystal layer has a twist angle in arange of 0° to 100°, wherein said incoming circulary polarized lightbeing linearly polarized at a surface of said first substrate in aplurality of directions repectively representative of said plurality ofwave lengths of said natural light to thereby create a display.
 5. Theliquid crystal display device as set forth in claim 4, wherein thecircularly polarizing unit includes, a first optical retardationcompensator plate having a retardation in a substrate normal directionset to not less than 100 nm and not more than 180 nm, and a secondoptical retardation compensator plate having a retardation in asubstrate normal direction set to not less than 200 nm and not more than360 nm, and the first optical retardation compensator plate, the secondoptical retardation compensator plate, and the linear polarizer platebeing stacked in this order when viewed from the liquid crystal layer,and |2×θ2−θ1| has a value not less than 35° and not more than 55°, whereθ1 represents a angle formed by a slow axis of the first opticalretardation compensator plate and either a transmission axis or anabsorption axis of the linear polarizer plate, and θ2 represents anangle formed by a slow axis of the second optical retardationcompensator plate and either the transmission axis or the absorptionaxis of the linear polarizer plate.
 6. The liquid crystal display deviceas set forth in claim 5, wherein the twist angle of the liquid crystallayer is in a range of 60° to 100°, the product of the birefringencedifference of the liquid crystal in the liquid crystal layer and thethickness of the liquid crystal layer is not less than 250 nm and notmore than 330 nm, and either the transmission axis or the absorptionaxis of the linear polarizer plate forms an angle, θ3, of not less than20° and not more than 70°, or not less than 110° and not more than 150°with an alignment direction of the liquid crystal molecules in a closeproximity of the second substrate.